Sorry to nitpick but You can definitely glass epoxy resin over a PU blank. It will just negate the lightness that you could achieve with eps foam. The reason why an eps/epoxy board can be stronger (besides the resin itself) is because the reduced weight of the foam allows you to have a more durable or heavy glass schedule with the whole board coming out the same weight as a lighter glassed PU/PE board.
Never glass polyester over eps. THAT will turn it to liquid.
It's really tough to see the "beaded" texture of eps foam through the fiberglass, but a good indication is to look right along the edge of the stringer, usually there will be little pockmarks that line the stringer because eps doesn't shape as evenly as polyurethane.
Your right - I had it backwards. No wonder why all my attempts to finish a board turns into a glob of jelly.