Downsizing at that particular time seems super unlikely.
I would refer you to the
Star League Sourcebook (FAS1630), specifically p.42, the last three paragraphs on the page under ‘Prelude to War’. According to that passage, that part of the reason for the Reunification War was to give
millions of soldiers across the five Great Houses who’d abruptly been put out of work by the formation of the Star League an application for their main skillsets that didn’t involve turning bandit.
What's your source for Davion formations immediately prior to joining the Star League,
Sadly, I can’t find an OOB for the AFFS pre-RW. (I’m certain
someone out there (apart from me) would be interested in seeing a product on the Davion Civil War, including full OOBs for the AFFS before, during, and after, but I doubt it would sell well enough to pay for itself.) I would note, however, that of the formations mentioned in
H:RW and
Field Report 2765: AFFS, none mentions that having a lineage going back to a pre-Star League ‘Light Cavalry’ formation, and knowing how fanatical military units get about their regimental traditions....
That said,
Historical: Reunification War has the AFFS shedding 37 regiments (and 23 WarShips) to SLDF colours, including the entire Terran Brigade and half the Syrtis Fusiliers (as a consequence of their backing the wrong horse in the Davion Civil War). It also specifically calls out the AFFS units assigned to the Auxiliary Corps: multiple Avalon Hussar and (remaining) Syrtis Fusilier regiments, as well as the Brigade of Guards, but
not anything by the designation ‘Light Cavalry’.
and could the 237th Light Cavalry have been a designation for troops donated to the SLDF campaign?
As noted above, the AFFS units serving in Operation BULL RUN seem to have retained their official permanent designations throughout, including the Avalon Hussars and Syrtis Fusiliers. The 237th are specifically referred to as an AFFS unit in every source I can find on them, which admittedly is not many — only
Periphery 1e,
FM:P, and
TtS:TP itself, so far. However,
Historical: Reunification War includes year-by-year Tabular Records of Movement of the regiments involved on every front of the War, and the listings for Operation BULL RUN on pages 142-145 don’t list a 237th Light Cavalry for the SLDF
or the AFFS. Indeed, for that matter
H:RW doesn’t seem to make any mention of the Sterope raid at
all. (Which is regrettable, but entirely understandable — like many sourcebooks, it had far more pressing uses for word- and page-count than detailing the origins of a single pirate band.)
Does one of those books actually say they took dependents along?
According to the very source that prompted my initial post:
The planet was discovered and settled in 2588 by deserters from the AFFS’s 237th Light Cavalry Regiment and their dependents after they fled the Reunification War.
Units that desert generally can’t go home to pick up their cat (much less their families) without getting arrested for said desertion, so they must’ve already been on the ships when the Sterope operation went pear-shaped. Ergo, either the 237th ‘simply’ brought their dependents along on their ships to spectate as they shot up a Taurian world (which is...
bizarre, but not entirely without historical precedent), or their going ‘over the hill’ was premeditated and prepared long before they actually hit Sterope. (You’d think that bringing their spouses and kids should’ve sent up red flags with anyone who saw them embarking, but then again....)