Okay...
These 'not turned up in post' were not random IMO
Why?
The people I know who got checked had confirmation emails with the ticket number on, the one they collected was this number +1
So as a hypothetical example, ticket allocated was 1222 and the ticket collected in person was 1223
Surely someone else would have had 1223? unless they specifically targeted collections and allocated 2 ticket ID's per person, one the club held and one they kept for collection