Close up of the stamps and postmark on the 87 delivery to The Black Museum .
The postmark is supposedly Croydon .
Only the 'ON' is visible and 'RREY' at the bottom .
The issues are firstly ,I've so far been unable to find a single known Croydon postmark from 1965 onwards that shows Croydon on the top and Surrey on the bottom .They all show CROYDON SURREY around the top edge .
Secondly, the date on the known postmarks for Croydon have the format
This envelope postmark shows the
Month [OV] for November followed on the same line by the year in full .
I'll post a few links of Croydon postmarks
November 1987 (same month)
Incidentally , you can clearly see previous postmarks on the two stamps from .... erm.... the last time the stamps were used .
Zoom on the left edge of the left stamp..... postmarked and yet only the stamp ... not the envelope .
Half the reason that a postmark goes over a stamp is so that these marks show and prevent the risk of the stamp being used a second time
You can lead a horse to water.....