Yes really, but perhaps your cards have been in fairly substantial envelopes.
I've worked for Royal Mail for a long time now and from time to time you see credit cards, driving licences, bus passes etc, etc that have come out of envelopes that have been processed through the machines.
Keep sending it by post as every letter helps for the company I work for, but make sure the envelope is well sealed and the card has a bit of protection too.
If you're getting it sent back by post I would advise that the card is well protected in the envelope; as sometimes the machines that sort the mail can have a nasty habit of chewing up envelopes with cards in!
It seems our American cousins have been publishing tickets sold as attendance for some years:
How Sports Attendance Figures Speak Lies - Forbes
This article from the Daily Mail goes back to 2008:
The truth behind football attendances: How clubs count on missing fans | Mail Online
For everyone talking about attendance records being broken, the club no longer publishes match attendances; it is now tickets sold.
Which also makes comparisons with other clubs records in this thread meaningless too, unless they report tickets sold too.