Douglas Johnson:

I've been told by a professional refinisher that you can't put poly
over an old oil and wax finish (I assume that's is what is there)
without a complete sanding. The wax in the pores of the wood will
keep the poly from sticking and result in a floor with cloudy specks
in it.

That is correct. Another advantage of shellac is that it will adhere
equally well to raw wood, wax & oil or old varnish. I considered wax & oil
but shellac offers greater scuff resistance. We cleaned and tested a small
area with shellac and it looks great. We plan to go ahead after we put
down the new kitchen floor.
--
Mac Cool