Thanks Geoff.
So the "real" value of these stamps is probably pennies, hence I get 300 for £10.
The seller on
ebay has answered my question and told me that they are CTO stamps - which I've had to Google.
It looks like these sorts of stamps are so widespread that 300 for £11, doesn't sound too outlandish and they could be real.
One more question I had is if CTO stamps from North Korea for the 1976 Olympics, were printed in c1976 and then cancelled or could they still be printed today in the same style as the 1976 stamps and sold en masse?
So my "1976" stamp was actually printed in 2024, for example....