The stamps I had bought from a seller in Great Britain arrived in the mail today.
I looked up the stamps on the envelope in the Stanley Gibbons catalogue. (It definitely seems like some stamp sellers have reams and reams of unused stamps from many years ago).
The black ink line across the stamps is the cancellation mark.
Aw. What’s up with that? I would like a proper cancellation mark showing the sending location and the date!

(15 July) Phosphorised paper
1330 801 Weightlifting, 29p multicoloured
1991 Scientific Achievements
(5 Mar.) Phosphorised paper
1549 991 Gloster Whittle E28/39 Aircraft over East Anglia (50th Anniversary of First Flight of Sir Frank Whittle’s Jet Engine, 37p multicoloured
2006 ‘Smilers’ Occasions
(17 Oct.) Booklet stamps (2nd series) Self-adhesive. Two phosphor bands. Die-cut perf 15×14.
2675 1932 Balloons (Ivan Chermayeff), (1st) multicoloured
2001 Regional Issue Northern Ireland
(6 Mar.) Printed in lithography by Walsall, two phosphor bands. Perf 15×14 w. one elliptical hole in each side
NI190 N7 Aerial view of patchwork fields, (1st) black, new blue and greenish yellow