Months names are all one off?

[Koen G]

In the manuscript that fragment is from, the paragraph about Luna and Aries clearly assigns Aries to March ("in Marcio est").

The Taurus part is a bit confusing.
"quia compotiste considerat Solem signa intrare a fine, iste a principio: Nam signum datur mensi, quem fine meretur."

I found it hard to translate this even with the help of ChatGPT, but I think it should be something like:
"because the computist reckons the Sun to enter the Signs from the end, while this one [Taurus?] from the beginning"

I couldn't get heads nor tails of this (no pun intended): maybe it means that regular Signs are entered from the rear end of the animal, while Taurus is reversed in its orientation (doubtful)? In this case, it has nothing to do with the month. 

The following phrase "each sign is given to the month that fine deserves it" feels ambiguous. Is the end of the sign in the month, or the end of the month in the sign? Or is fine just something like "in the end"?

Then in paraphrase it would be something like: "Astronomers reckon the Sun enters the Signs at the end, but this one at the beginning. But at the end, the Signs are given to the month that deserves them (i.e. the "correct" month).