I think hidden chainplates exist on several Pearson models, based on the few I've seen. My current guess is they're partly behind the wooden enclosure housing the cabin speakers, but there's 'stuff' sealing those to the surrounding fiberglass, as well as screws that look like they've never been turned. I could always experiment, but in the middle of sailing season there's this trade-off: Keep sailing and risk a problem - or open things up and risk losing the season...
I consulted with my business partner and he confirms that the chainplates are behind the wood panels. It should be fairly simple to get at them.
Don't be afraid to dig into this sort of stuff on your boat. You need to become familiar enough with the boat so that you have the confidence to, at the very least, know what you are paying others to do for you should you choose that route.
If you see evidence of leaking, ie heavy rust stains, then you need to address it.
Remember, chainplates usually always break where they pass through the deck. Moisture is trapped in there and there is a lack of air circulation and the chainplates will develop cracks. Next thing you know. They break.
If you do see signs of corrosion and decide to pull the chainplates for a closer inspection. Replace them. And the bolts. Even if they look okay. It's not worth going to all that trouble and putting the old ones back in. New chainplates, especially stainless ones aren't that expensive.