OK guys, here are some real questions :-) :

If one hold TIAA Tradiational in an IRA and later converts some/all of that IRA to a Roth, are the original vintages preserved or is the conversion treated as a sale in the IRA and a new purchase in the Roth?

How about when a 403(b) is rolled over into an IRA?

Yes, I know I can ask T-C.  And I may do so.  But this seems one of those cases where the expertise of this board might really shine.

TIA.

P.S. The reason I am asking is that, like many folks, I am thinking of putting money in Trad (a first for me; heretofore I've been exclusively REA) and looking down the road to see if the current great vintage is only as good as long as I keep the funds in the current accounts.