For Sale: 62cm Raleigh lightweight products division 531 C Luxe frameset

That fork crown was pretty common on mid-80s/early-90s Raleighs; at least, I've seen a few of them. Don't remember anything about the lugs though!

If you're wanting to tell whether a frame is 531c or not, a 531c frame will always have a 27.2 seatpost (or more correctly, a 531c (or comparable quality) seattube will always take a 27.2 seatpost, and a frame with a 531c seattube will almost certainly be 531c throughout).

That seems a bit general. Are you saying that if a frame takes a 27.2 seatpost, then it is 531c throughout?