That's a good reminder, that perp/s possibly had to look for and find at least one belt. The housekeeper mentioned that the bedroom was more untidy than usual, that may reflect a search.my impression was that someone may have sat on a made/unmade bed while thinking about the belts. IMO
IF it was someone who had knowledge of the household, they'd have known where to look for belts immediately. IMO
Seeing as they still had their coats/jackets on, highly unlikely that HS had gone to bed that evening. IMO
ETA: Just saw some other posts re: bed. Maybe it was all or maybe it was irrelevant. IMO
I've read about intruders using electrical cord (ripped off toaster or something) or a scarf/coatbelt from a front hall closet, but not so much searching bedroom closets and drawers for a belt. And, of course, if something was brought to restrain wrists, it seems extra rope could also be brought. Possibly a belt was brought, that would be hard to figure out: was it Barry's, Honey's or the perps?
If the second belt was taken from the bedroom, to me that seems very clear evidence it was staged m/s. To go to that trouble of searching the bedroom, that seems like a detail someone wouldn't make any effort for, unless they were trying to make it look like Barry's actions.