The Schoeps M 221 series was produced over a span of about about 15 years and encompassed some eight or nine different capsule types, depending on how you count them. Those capsules were hand-assembled (as capsules still are at Schoeps), and over the years small changes in production occurred for any number of reasons--some sonically motivated, some not. On top of that, the capsules of the series are now in the age range of 40 - 55 years old, so differences in condition can throw a large randomizing factor into any attempt at comparison.
Thus I really doubt whether any valid conclusions can be drawn today about the sound of the "A" vs. "B" series microphones in general. We have the microphones that we have, and they sound however they sound. At the very least one ought to compare microphones with equivalent capsule types rather than speaking of entire series in general, no?
And by the way, there were at least three other varieties of M 221 that were neither the "A" nor the "B" type: the type that was made before the "A" was applied, a type made for Telefunken which has some aspects of both, and a type also made for Telefunken which had a completely different ELA model number but was still a kind of M 221. The "Schoeps Classics" Web site doesn't say everything that Mr. Vollmer knows ...
--best regards