Earlier this year I booked a standard room at a HGI and was upgraded to a accessible suite on the first floor. This may not be standard practice, however, since I always ask if an upgrade is available if the FD does not bring it up first. It's possible that they were originally going to put me in a standard king; I just don't remember how the conversation went at check in.

I was there for several nights. I think if this happens again, I'll tell the FD to kick me back into a standard room if at some point during my stay another guest needs an accessible room.

EDIT: Come to think of it, if someone was trying to book an accessible room, the website is not going to know if someone in an upgraded accessible is willing to switch back to a standard.