When I rolled over a 403(b) TIAA-CREF GSRA to an existing TIAA-CREF IRA in 2005, I was required to fill out a form headed "Request for a Payment".  Much of the form was pre-filled in for me by a rollover expert in Charlotte.  The form repeatedly uses the term "withdrawal" to refer to what's happening to the old accounts.  I don't think I gave that enough thought at the time. But it now seems clear that even though the rollover was within TIAA-CREF, I gave up my vintages in TIAA Traditional.

On the other hand, when TIAA-CREF involuntarily moved my RA after-tax contributions to a new, after-tax account (first ATRA, now RA again), they eventually assured me (when I inquired specifically) that the vintages there had been preserved.

In any case, it's next to impossible to verify any of this, because your statements don't break out holdings and income by vintage. Even if someone isn't making contributions anymore (which slightly simplifies the calculations), taking a starting and ending balance one year apart doesn't provide any way to extract the various interest rates that lead to whatever Rate Of Return (for the total sum, that is) you manage to calculate on the two numbers.

Tim