Yeah, still hung up on that whole span for Succession Wars? The Starslayer resumed production during the Clan Invasion and per pre-Invasion scenario book about the Big Mac, some models were recovered and in use.
Per TRO: Clan Invasion
Blue Shot resumed production of the Starslayer in 3056, upgrading to the STY-3C, which uses an endo steel frame to allow it to mount even more armor than the Crab.
That's four years after the Truce of Tukayyid halted the Clan Invasion and is confirmed on the MUL.
As for McCarron's Armored Cavalry. The Scenario Pack causes continuity problems. The fluff for the Starslayer is for an older version without advanced technology. It says
Lacking ferr-fibrous armor and endo steel, the Starslayer is rarely used. With recent advances in 'Mech technology, more Houses may pull their few Starslayers out of mothballs and recondition them.
The TRO entries also talk about an older less advanced variant. The first scenario using the Starslayer takes place in 3044. It lists the 3C being used.
Now I will admit that it is possible the Big Mac upgraded their Starslayers. They had the money and tech to do so. And it could be that Blue Shot Weapons made the variant official. However there's still an official 12 year discrepancy there. Even as a custom job, they still wouldn't be available for the Clan Invasion as they're exclusive to the Big Mac. Unless you want to go with the
maybe of the Houses pulling them out of mothballs and upgrading them, which would still have date issues.
The mechs not in these TROs are not getting cut from canon . . . just de-emphasized, they are still on the MUL and some are still on RATs or used in other official sources.
I sure hope not but does their being listed on the MUL if stats or RS aren't available?