The TLK always has a index part number as it's last field.
At the moment the TLK also contains the payload fields, but it shouldn't they're not useful (see HPCC-24713).
So the TLK format should be
Once published clients (and dafillesrv) can ensure that the correct format is returned when reading the TLK.
In particular it can return the index part number, so that clients can use the TLK to look in the right index parts.