Its also interesting that the 531 decal is very good condition but all the other decals are missing one has to wonder if its a re-paint & these have been added afterwards, pulling out the forks & possibly seeing the original colour on the stem may show its original colours.
My old Raleigh has the usual 3 rivet fixing badge, I'm not sure when they adopted the bonding method.
I have three old bikes around the same age, (my friend has one also) all look same lugs all different types of serial numbering, late 1980s early 1990s there were a few major manufacturers making frames & so many companies then adding their own badges equipment etc. As I mentioned before seat post sizing maybe good start on detective work.