This is something I've known about for a while, but if I've blogged about it before, I've forgotten. And I didn't tag it with my MU tag if I did.
So, Magic-Users. How many spells per day can they cast? Apparently, as you level up, there are quite a few discrepancies depending on what book you're using.
My print version of the Mentzer Expert Set has this table:
Up to 5th level, they're identical. But at 6th level, you get an extra 1st level spell in my print book than in the PDF version.
7th and 8th level are the same. So far, slight advantage to the print book.
At 9th level, though, the PDF version gets an extra 3rd level spell compared to the print book. Now the tables have turned!
At 10th level, the print MU gets an extra 1st level spell, but the PDF MU gets an extra 4th level spell!
But at 11th level, the PDF MU finally gets that fourth 1st level spell, and their first 6th level spell. But the print MU gets extra 2nd and 3rd level spells (fourth for each) and finally gets that third 4th level spell.
12th level finally sees the two versions the same again.
But at 13th level, the print MU again gets a 1st level spell that the PDF MU doesn't, which remains the case at 14th level, as well.
I don't know if the PDF was edited to match the later RC progression, or if there were multiple versions of the Expert Set put out. Here's the RC:
And for completeness, here's the BX version:
This is almost the same as what's in the PDF and RC, until 12th level. Then the BX MU gets a boost in their higher level spells per day. Since the BECMI line was planned from the beginning for a level 1 to 36 spread, that's not surprising.
AD&D, of course, also has a different spread of spells per level:
Not gonna analyze all the differences between AD&D and Classic, as I'm mainly just interested in the two very different versions of BECMI Expert today. Oh, and just the BECMI MU. The Elf is also different, with a progression matching the MU in the PDF version 100%, but in the print version getting 10th level spells 5/4/3/2/1 in the print version!
Either way, the spell progression of both print and PDF Expert sets match up with the progression in the Companion Set (which matches the RC, at least at 15th level):
The print version gets a bit more versatility over all, with more lower level spells sooner. But the PDF version gets better higher level spells, so more power.
Just for fun, I may go through my spell tables and see what it would look like to give the most generous spell progression for each spell level, mixing the two (three with BX) Expert Sets. Or maybe even bringing in the 1E progression, too! Just to see what it's like.