As sassir pointed out in his comment this isn't really a matter of spelling rather than a matter of rasm al-mushaf (how words/letters of the quranic text or scripture have been written by the sahaba and later).
You should know that the Arabic letters and language as we know it today was not the same as at the time of our Messenger (Peace be upon him) so the nearest version to what the scripture looked like in it's original form (the way the sahaba wrote it down) in a mushaf looks like this:
Note that at the time there was no punctuation, so some letters which now look different were similar at the time. The word above as written may mean "the two worlds" if one reads it العَلَمَيْنِ instead of "the worlds العَالَمِينَ" in modern Arabic the correct spelling would be:
now the point is that the scholars say that the original scripture is what we may call "canonical" many scholars said the quranic scripture shouldn't change and be kept or preserved as the sahaba wrote it, so a way to correct the (historically) "false" scripture was adding a pending alif "ا" in the mushaf (copy of the Quran) to avoid changing the canonical text.
For further information i strongly suggest you to check the following posts:
What are the readings (qira'at) of Quran?
How to explain the recitation لَئِنْ انجــينا (verse 6.63) by Al-Azami in his book “The History of the Quranic text”?
Why do words like "salah" and "riba" have an extra unpronounced letter waw in them? -> clear difference in scripture and rasm (?).
Answer of the updated question:
The rasm of the mushaf or rasm al-'Othmany as it refers to the quranic text or scripture written following the orders of the Caliph 'Othman by a chosen comity of sahaba who have been Quran memorizes is as said standardized or unified, so it's canonically only one rasm. (See for example this or this fatwa saying it's mandatory to keep it and forbidden to change it).
But and here I might add a few information that came into my mind now:
When you read in different mushafs with different readings or riwayat you may find some different symbols: For example the pending alif as in your example may refer to a different qiraa'a (reading) (a prominent example for that would be singular/plural) as some qiraa'at had slight differences in letters like added letters, subtracted letters or replacing a letter by an other you may in the actual copy's you hold in hand have "different" spellings or scripture I think I've pointed at some examples already in my answers on the linked questions, but you could also check my references. If you need further information feel free to ask by comment.
Here some Arabic references:
Fatwa whether it is permissible to change the rasm (write in modern Arabic orthography), a study on rasm, introduction on rasm , some examples and "secrets" of rasm.
And Allah knows best!