It should work regardless of what version of Trainz you are using.
I don't know if the person you got the certificates from was using an older version of Trainz below TANE SP3 (min version required) or a newer version so I can't say if that's the cause. What I can suggest is clicking on the provided certificates to bring up the details and check to see if its still good or was it expired. TANE SP4 for me shows they're good until 4/8/2028 (in fact, that's for all versions of Trainz at this moment).
TS12 works, and so does TS12 SP1 as I got its online services working awhile back so I was able to download my purchased items into the game (not a fan of SP1 for TS12 due to bugs and general performance issues it came with). Link to that is in post #1.
They were from me TANE SP4 expiry 08/04/28 or in US format 04/08/28