In earlier editions there was a limit to the amount of spells a magus could copy from another text based on his scribe latin score. In 5th I see on page 102 a section on copying lab texts. I assume that this is the rate that a magus if given access to a library that has lab texts is the limit one can copy er season.
Profession: Scribe x 60 per season.
I don't see any other place in the core book that states spell copying anywhere else.