"TGXXX serial numberin a reflective type etching just outsife of the clear plastic hub (still towards the inner ring of the disc though) if you bought a pack you should be able to see it, but in the package, it's actually obscured by the spacer"
I have had luck reading the serial numbers in the gaps between the white octagonal spacer and the round inner silver hub ring of the top disk.
It is pretty difficult, but possible. When you shake the pack the octagonal spacer spins a fraction of a turn revealing more of the hub.
It probally is not necessary as every pack that we have seen with an octagonal space has been TY T02.