A 3+3 reed block configuration is common in French style accordions (with very small buttons) and in large bayans.I always thought that "standard" CBA reed block config was in 3 row groups. "PA with CBA keyboard" boxes are less common, unless there's a cassotto?
In any case, it's not just the reed blocks - a 5-row CBA keyboard is quite a complex thing to take apart and put back together again. Even if you don't have to glue & unglue buttons.
Looking back, I should have picked a diddley bow as my instrument. Easy to service & matches my musical talent level.
When you buy a CBA that has a PA relative (take for instance the Bugari 508 CBA versus Bugari 288 PA) you get exactly the same accordion, but with a button keyboard (where otherwise the PA keyboard would be) and all the positions on the reed blocks filled to give you 46 notes.
(I have an older Bugari 508/ARS/C which does not have the same body as the 288/ARS/C but this one still has 2+2 reed blocks.)
Contrary to what seems to be common belief a 5-row CBA is no more difficult to take apart and put back together whan a 3 -row. There is a clever hinging mechanism to couple row 1 and 4 and row 2 and 5 that is all in one piece per note. So the extra work is mostly in unscrewing about 65% more buttons (and screwing them back in).