The Mushafs of the sahabah
From your question, one can see some misunderstandings and misinformation. Allow me to briefly correct a few things:
- A Mushaf is the book that one holds in hand that includes the qur'anic text. Today: based on one of the accepted qira'at.
- Variants of a Mushaf shouldn't exist, but variants of a qira'a actually do.
- When we talk about the Mushafs of sahabah() generally the speech is about the following content:
- the amount of surah's,
- whether some surah's were added or missing (for example ibn Mas'ud didn't compile al-Fatihah).
- whether a surah ended as in the Mushaf al-Imam or it was extended by another surah, meaning the sahabi has merged two surahs in one as Ubay ibn Ka'ab apparently did with suarah al-Fil and Quraish.
- the order of surah in the Mushaf (As far as I know only Ubay ibn Ka'ab was mentioned to start his Mushaf by al-Fatihah).
- whether all surah's except with Bara'ah (al-Tawbah) started with "basmalalah" (Bismillahi ar-Rahmani ar-Rahim) or only al-Fatihah or none.
- Some additions or missing or permutations or usage of (different) words.
So, from this perspective, it is easy to reclassify a Mushaf as of any Sahaba if we have reliable information about their Mushafs. However, this is not the case. Since all chains of transmission of the reports of those who saw these Mushafs are interrupted and discontinuous. However, we only know about a few peculiarities and deviations, and our information about them is incomplete.
The case of ibn Masu'd
As early as the 4th Hijri century, many scholars stated that they were shown many so-called copies of the Mushaf of ibn Masu'd, where one did not even remotely resemble the other.
Among what we know about his Mushaf is that he neither compelled al-Fatihah in it nor the two 'Muwaidat (Surat al-Falaq (113) and an-Nas (114)).
For example, ibn Ashtah ابن أشتة (died 360 a.H.) reported a statement from Jarir ibn 'Abd al-Hamid (died 188a.H.) جرير بن عبد الحميد بن قرط that the following order of Surahs (an extract) in Mushaf ibn Mas'ud as a-Suyuti mentioned in his al-Itqaan (In brackets you may find the order of the Mushaf al-Imam):
- Al-Baqara (2)
- an-Nisa' (4)
- Aal 'Imran (3)
- al-'Araaf (7)
- al-An'aam (6)
- al-Maidah (5)
- Yunus (10)
- Bara'ah (9)
- an-Nahl (16)
- Hud (11)
- Yusuf (12)
- al-Khaf (18)
- Bani Israel (al-Israa') (17)
- al-Anbiyaa' (21)
- Taha (20)
- al-Mu'minun (23)
- a-Shu'araa' (26)
- as-Saaffaat (37)
- al-'Ahzaab (33)
- al-Hajj (22)
Note The book of ibn Ashtah is among the missing jewels of Islamic literature.
While al-Nadeem (also known as ibn an-Nadim died 380 a.H., a shi'a scholar) in his al-Fihrist كتاب الفهرست reported from al-Fadl ibn Shadhan الفضل بن شاذان (died 260 a.H. a Shi'a scholar and an expert of qur'an according ibn Nadeem) describing a Mushaf copy attributed to ibn Mas'ud the following deviation in order of Surahs compared to the above:
- Bani Israel (al-Israa') (17)
- al-Anbiyaa' (21)
- al-Mu'minun (23)
- a-Shu'araa' (26)
- as-Saaffaat (37)
- al-'Ahzaab (33)
- al-Qassas (28)
- an-Nur (24)
- al-Anfaal (8)
Ibn an-Nadim added that in some reports surah a-Tur (52) was compiled before surah adh-Dhariyat (51). Both al-Fadhl ibn Shadhan and Jariri ibn 'Abd al-Hamid reported at-Tur as the 64th surah in the order of ibn Masu'd Mushaf. While adh-Dhariyat was reported as 63rd by al-Fadhl, ibn Jarir reported it as the 65th.
Both reports only count 108 Surahs.
As for what you refer to as variants of his Mushaf I assume you mean variants of what he taught people in regards of recitation or qir'aa'. This actually is present to some extent in several tafsirs and other resources of 'uloom al-Qur'an and hadith collections. You may find some examples of this kind in my answer on What are the readings (qira'at) of Quran?.
Here just a few examples of qira'at attributed to ibn Mas'ud that are among present in the riwaya of Hafs:
Indeed, the religion in the sight of Allah is Islam. ... (3:19)
إِنَّ الدِّينَ عِنْدَ اللَّهِ الإِسْلامُ
Except with al-Kissa-i all 10 qurraa' pronounced it as shown, whil al Kissa-I recited it:
أنَّ الدِّينَ عِنْدَ اللَّهِ الإِسْلامُ
And [Joseph] said to his servants, ... (12:62)
وَقَالَ لِفِتْيَانِهِ
This is the reading of Hamzah, al-Kissa-i and Khalaf and the riwaya of Hafs, while the rest of qura'a and rawis recited:
وَقَالَ لِفِتْيَتِهِ
They and their spouses - in shade, reclining on adorned couches.
هُمْ وَأَزْوَاجُهُمْ فِي ظِلَالٍ عَلَى الْأَرَائِكِ مُتَّكِئُونَ
This is another reading attributed to ibn Masu'd and it was followd by the 10 qura'a except with Hamzah, al-Kissa-i and Khallaf who recited it:
هُمْ وَأَزْوَاجُهُمْ فِي ظُلَلٍ عَلَى الْأَرَائِكِ مُتَّكِئُونَ
Why the restriction on the above points when mentioning the qur'an of the sahabah?
The sahabah witnessed the revelation of the qur'an, so those who were able to write may have had their own Mushafs, with deviations to the final version. As parts of the revelation was abrogated from time to time.
The final version is called al-'Ardah al-Akhirah which was witnessed by many sahabah(). So even if some sahabah had deviations in their (own) Mushaf copies they knew what content was still part of the qur'an and what was no longer part of it.
After the death of the Prophet() the sahabah agreed that it was necessary to canonize the qur'an first by gathering all parts of written quranic texts and this way confirming the 'Ardah al-Akhirah in the era of abu Bakr(), secondly by arranging it and creating different copies which were sent to some major regions to have a backup and a standard in the era of 'Uthman.
The Mushaf al-Imam which was introduced at the time of 'Uthman was a standard that, was agreed upon. From now on it was no longer allowed to deviate extremely from this standard. For example, descriptive (tafsir) or synonymous readings were no longer permitted. Since 'Uthman ordered to use the usage of the language of Quraish when in doubt, other language variants were eliminated in many places. Some scholars regard this restriction as meaning that only one of the originally 7 (permissible) ahruf is present today.
The rule for accepting a qira'a is for example explained in: What were the criteria for validating a qira'a? or Variant Reading in Quran 62:9
After the compilation of the canonical standard Mushaf al-Imam and sending it out to the major regions of Islam. All Muslims were ordered to burn their previous copies to avoid mixing. That's why we may say that the Mushaf's of the sahabah should no longer exist. As a matter of fact even the original copies of the Mushaf's sent out to the regions nor the Mushaf al-Imam which remained in Medina exist with enough certainty. All old or early copies of Mushafs existing today are rather of the 1st hijri century or later. So they may have been compiled or copied after the time of 'Uthman.
At the time of the sahabah () and even the time of Tabi'yn the qira'at as we know were not yet known. Each of the accepted qira'at we have today
originates from one of the qira'at a sahabi taught.
For example, even if ibn Mas'ud who lived in Kufa at the time 'Uthman ordered the Mushaf al-Imam initially rejected it and taught people the qur'an as he was doing before for a while he accepted it later. But we can still find fragments of his qira'a in the reading's from al-Kufa for example the qira'a of Hafs is basically the qira'a of 'Ali ibn abi Talib in a more Hudahaly pronunciation, because in contrast to the Hijazi people like the Quraish, the members of the Hudayl tribe - to which ibn Mas'ud belongs - use the "Hamza" excessively in their language.
Still at the time of 'Uthman the qur'an was written in a scripture that sometimes is called al-Khat or ar-Rasm al-'Uthmany. Diacritics were still unknown and there was a huge chance of "mistake" for none-Arabic speakers who at least were familiar with the Arabic scripture since different letters were written similarly. So the Arabic scripture was improved by improving the Mushafs for learners, first by adding a dot to show "vowels" and then by distinguishing similarly written letters like (ب,ث,ت,ن or ذ,د or ز,ر,ن ...) and by adding diacritics.
See also the following posts with some more information and examples: