Mr. BoH
I've been talking about that sort of issue for some time. It's actually a known issue on some of the LD trains (e.g. CHI-SEA requiring a room change at MSP or Williston, CHI-EMY requiring a change at DEN, or WAS-CHI requiring a change at CVS, CIN, or PIT). Arguably it's less of a risk in a larger body of spaces (the CVS/CIN example is problematic because the Cardinal has generally only had a single sleeper, so you have three bedrooms and about eight roomettes available, whereas non-Quiet Car Acela Business has three cars of about 60 seats (so 180 spaces normally/90 under present circumstances).

One of the issues under normal circumstances is also that there's a big difference between being told, say, "When traveling BOS-WAS, you'll have a seatmate NYP-PHL" and "You'll have four seatmates at different times". On the Regionals in BC, coming from Virginia, it isn't uncommon to have a batch of people boarding at ALX (or even at WAS when going to BAL) but there's no "easy" way to check that.