Do we actually know which of the terms Musa () completed?

Question

In surat al-Qassas a long passage tells us the story of Musa (). In the part telling what happened after reaching Madyan, we learn that he married one of the daughters of the old man under the condition to fulfill either a term of 8 years or 10 years. But the story no where tells us which of both he has achieved. Allah the Almighty says:

He said, "Indeed, I wish to wed you one of these, my two daughters, on [the condition] that you serve me for eight years; but if you complete ten, it will be [as a favor] from you. And I do not wish to put you in difficulty. You will find me, if Allah wills, from among the righteous." (27)
[Moses] said, "That is [established] between me and you. Whichever of the two terms I complete - there is no injustice to me, and Allah , over what we say, is Witness." (28)
And when Moses had completed the term and was traveling with his family, he perceived from the direction of the mount a fire. He said to his family, "Stay here; indeed, I have perceived a fire. Perhaps I will bring you from there [some] information or burning wood from the fire that you may warm yourselves." (28:27-29)

Do we know at the end which of these terms Musa could fulfill?

Answer 1

The hint of @Ahmed helped:

Narrated Sa'id bin Jubair:
A Jew from Hira asked me which one of the two periods Musa (i.e. Prophet Moses) completed. I said, "I don't know, (but wait) till I see the most learned 'Arab and inquire him about it." So, I went to Ibn 'Abbas and asked him. He replied, "Moses completed the longer and better period." Ibn 'Abbas added, "No doubt, an apostle of Allah always does what he says."
(Sahih al-Bukhari)

The hadith was also compiled by al-Hakim from Nishapur in his al-Mustadrak, al-Bayhaqi in his as-Sunan al-Kubra, and ibn abi Shaybah in his al-Mosanaf. Ibn Hajr mentioned that it also appears in at-Tabrani's al-Awsat.

The statement:

"Moses completed the longer and better period."

as understood, interpreted and -in the translation more- clearly refers to the longer term of 10 years.

Answer 2

This Jewish Midrash, if I understood it correctly, tells that Mose fled from Egypt to Midian when he was 20 years old and left for Egypt when he was 60 years old, when all people who prosecuted him were dead. According tho this, he stayed there much longer than the 10 year period.

It is told in the Torah that he was 80 years old when he lead the Passover, so this very large span would even be in range.

An oath is also mentioned in another Midrash but not the condition we know from the Qur'an.