I have only discussed with one (Dutch) TA agent. Had booked biz flex ticket, which he first upgraded to D (for an extra 1000 eur) and then did the P upgrade using points. I made another phone call later and asked, if I could use the vouchers, it was agreed, the points returned and the reservation remained confirmed 1A both ways between (HEL) CDG and GRU. Later I made a similar biz flex resevation for my mate for the same flights, called TA, the agent remembered me, did a D upgrade, and then a point upgrade to P, 1L both ways.
I guess you were lucky as it’s not what has been communicated
