When we had an estimate for new kitchen flooring the installer opined
that our vinyl flooring probably contained asbestos (ca 1981) therefore
they
couldn't remove it. They would put down a 1/4" of plywood then the new
flooring over it.

Q1: Would vinyl from that era really have asbestos?

Q2: Is the plywood over the existing floor reasonable?

Q3: Would the asbestos create a resale problem? (Asbestos was common
when I grew up.)

Asbestos was banned in the late 70's although existing stock was allowed to
be used. You're right on the borderline, so you may want to have it tested.

It is not a resale issue if it is in good condition. I have asbestos (5%)
tiles in my basement. I could very well have (1%) asbestos in my drywall and
joint compound, though I've never tested it. And I have lead solder in my
pipes....