I have numerous Weaver cars and have applied both Pollyscale brushed on flat finish or Dullcote lacquer sprayed finish and never had a problem with the lettering/numbering on these cars. I recently purchased a 2 bay Virginian open top hopper car that Bob Weaver must have produced in the 1980's, this car has faint spotted white lettering(similar to an older water slide decal with area's that the base car color shows thru), no reporting marks on the end corners of the car, no trucks/couplers and packaged in the small Weaver cardboard box, the letter and numbering color was a faint white/gray.
I started to brush on the Pollyscale acrylic flat finish on two letters, A & N, and the letters dissolved. I had some 7/16 inch white gothic letter decals that were trimmed on the decal sheet to approximate the dissolved letters, I applied these letters, used the decal setting solution and I had to mix a faint white/gray acrylic paint and brush paint over the bright white decal letters. The results were not perfect but acceptable.
This leads to my question, were the early Weaver cars stamped or imprinted in a water soluble ink? This car was not a unpainted car, the Weaver box was marked Virginian, also this car came with end slope sheet braces that had to be glued to the endslope sheet and end frame.