My best guess is (without any evidence or substantiation) that this was affixed by a local dealer or shop (there were dozens of Laser dealers in the UK in the 70s) when they sold the boat, in a similar way that a car dealer would put their own stickers on a car they sold. I think the dealer would have put the badge on as "evidence" of their quality etc.
Do you have a zoomed out photo showing the LPE sticker, which should be just above there?
A little Googling has found further examples of this badge on other boats (not Lasers but a keel boat and a powerboat).
I suppose it is not impossible that LPE did have a period when they fitted these badges for a time....but I have seen so few of them on Lasers it seems unlikely and, in my opinion, more likely to have been fitted at point of sale by the dealer.
It wasn't actually even PSE before 1983, just "Performance Sailcraft", one of the branches of the worldwide builder. I just looked at a few of the oldest boats at my club this past weekend, and their builder's stickers (if they have any) don't say anything of their origin. We got boats from both Ireland and England in the 1970s, but there's no way to tell which came from where.
The number on the SBBNF plaque won't mean anything really; it's what's under the bow eye that gives away the boat's vintage.
Yes, I have to fund the number. I have to hulls with red ciba geigy glue. But I dont have any origin of production. But I also have a hull from Banbury (sticker), an its molded with polyester and rowing mat. So I presume that Waterford used red glue, which was a great failure and caused bankrupsy om early 80s. I have seen a 1982 boat and it has a stronger glue with different colouir.