I know it's too late for correcting things like these, but in the latest PDF that I got I noticed that on page 50, "Magus Only - after Apprenticeship" section, it seems to remind the limit for maximum arts, but the limit is not explicitly said. In the old Arm5 book, p.32, there was this line which is here not included: "A sensible maximum for a magus’ Arts is 10 plus one for every four years since apprenticeship." This line was deleted just before "Thus, a magus who is 20 years out of apprenticeship..." Maybe you should at least update the PDF.