At a condominium sub panel, which fed by 3 wires from a main disconnect only, where there is NO main panel dedicated to subject sub panel, is it still allowed to bond ground/neutral bar to the sub panel' s chassis?
You have a 4-wire feed
You actually do have a separate ground wire, even though you can't see it. It's the metal pipe the wires run in.
Commercial scale buildings like that usually use conduit for feeder. And 1985 is before PVC came into vogue. So almost certainly, this conduit is metal and non-flexible, and is the valid and proper grounding path. I have four large buildings with not one green or bare wire anywhere in the complex.
Still unclear on if this is a main or sub panel
You need to check with the condo association about where exactly your neutral-ground bond occurs. If there is a main breaker down in a utility room somewhere, it is assuredly there. But you have to ask.