Remember that the code is from the perspective of the issuer; not the taxpayer.

A code T in box 7 of 1099-R is for a Roth IRA distribution, when an exception applies.  It is used for a distribution from a Roth IRA if the IRA custodian does not know if the 5-year holding period has been met but:

• The participant has reached age 59 & 1/2
• The participant died, or
• The participant is disabled.

So, they don't know if there are/have been other, earlier, Roth account(s) and the tax program doesn't know if your taxpayer took out Basis or more.