A yuuuuuge amount of the stuff in P-H Books 1 through 10 can be played on a 26/72. A ton of that stuff, including up through books 9 and 10, is folk or folk-based music you can work out for 26 keys on the treble as well as 72 basses. Tangos, gypsy/Hungarian, Ukrainian, all kind of great music totally playable on a 26 treble and 60 or 72 basses. I never want to look at or hear the "Clarinet Polka" or a John Philip Sousa March again. Ever. But there is some gorgeous world music in those books--I play stuff from Books 7 and 9 on small accordions all the time. And there's an awesome Ukrainian dance in Book 10.
On the treble side, you rearrange the spots that go above "High C," or below the "middle B" that is the lowest note on a 26. And you simplify the basses some when the piece is in keys where basses at the far right are doubled over at the far left for those keys.
Especially if your 26/72 has LMM. You can just flip on one of the registers that has the "L" reed in the mix and play low stuff that has notes you're missing on a 26. Like the L switch, the LM switch, or the LMM switch. But with your hand placed the next octave up where you do have enough notes. The low reed sounds an octave down, and nobody will know the difference.
Now, if you're aiming to take lessons or otherwise seriously learn all the technique through the P-H series, you'd probably want something with more treble reach and more bass reach. Yes, the more advanced grades call for 96 or 120 basses and 37-plus treble. But if you didn't want to go bigger, you could still make serious headway through most of those technique lessons on a 34/72. Or a 30/72.
