many bonds were sold at less than par value (face value at maturity) the difference between what you paid to buy it and what you would get paid at maturity is OID. OID is amortized over the life of the bond and added to the principal (what you paid)
so your basis would be what you originally paid + the OID. if you sold it or it was called before final maturity and you got less than this total you report a capital loss if you get paid more you have a reportable capital gain. if it reached maturity, then there should be no gain or loss but you still should report it because TIAA is probably reporting it to the IRS
it is also possible the issuer went bankrupt which would make the obligation worthless. you would report a capital loss = what you paid + the OID.
if none of this applies contact TIAA, to get the whole story.
if you were not the original owner of the security, then the Original Issue Discount reported on those 1099's likely needed to be adjusted each year
