As Tom say's it's more likely a void in the Ply and this can happen during the laminating process.. But nothing wrong with treating all your parts, it just means it will take longer unless you coat larger built area's rather than individual parts.

I live in a old house which before we restored it was riddled with Woodworm and Death Watch Beetle. So I have some experience in this matter
Woodworm has a 4 year life cycle and you don't see the entrances only the exits, so if they are woodworm exit holes those Eggs were laid over 4 years ago and those adult beetles are long gone, they don't stay around laying more eggs but go on a mating flight. So the way to know if you've got woodworm, is beetles at your windows in the summer trying to get out to find a mate, rather than holes. This means that the ply itself was lying around over 4 years ago in a susceptible environment, which in itself is unlikely as it was probably only made in China 6 months ago. I would also say that woodworm are quite fussy about the density of the wood and the ply cores are far too soft for their tastes. They tend not to infest Plywood, Chipboard, MDF etc as they like their grubs to have something solid to munch away at for their 4 years, so go for medium hardness solid wood.
Cuprinol is nasty stuff it stinks for weeks if not months and attacks glue bonds etc. and may affect the ply bonding itself and to be honest doesn't penetrate deeply enough to work that effectively with just a brush coat.
I had a lot of pits and holes in the edges of some of my Victory X-Section Ply and these are caused by the laser cutter burning away the more vulnerable soft core layers or as Mr T says voids introduced during laying down of the ply which would not be visible until it was cut.

You could say that you might end up opening a can of worms if you do use it on a model..

Hi Captain D

There is another chemical free way to kill woodworm which might work for model ship wood.
My previous employer owned a wildife park and also a large collection of antique furniture much of it peppered in woodworm. His solution was to put the furniture in the walk in freezer we kept the frozen meat for the big cats in. After a minimum of 48hrs any woodworm and their eggs were dead and gone!
It didn't affect the furniture so it might be possible to do the same by leaving the kit wood in a domestic freezer for the same time. I would experiment with the scrap pieces of ply first, if they do warp you might get away with clamping them between thicker wood panels for support?

Cheaper than Cuprinol anyway!

Robin