You aren't going mad, when we had the 55504430 OS sent in for support there was no trace of it on TIS (and still isn't).
The release order went.

55503875 - On TIS older
55504430 - Ghost
55508105 - On TIS current

The only thing I can think of is some vehicles came with 55504430 new but got updated at the dealer before delivery (or that was the intention).
Either way TIS doesn't know about it that is for sure.

Part Number CVN Description
55508105 00003A0D New software with diagnostic enhancements for DTCs P11B3, P11CC, P1476, and P22FE.
55503875 0000C880 New software with improved EGT tampering strategy.
55488069 0000CA69 New software for start of production << Earliest we've seen in a truck
55500006 00004875 New software for start of production
55488063 0000F08F New software for start of production
55488052 0000837F Main Operating System