I suppose it’s irritating that you pay (a likely large amount of money as it’s probably a UK ticket) for a ticket with a seat reservation, the least they could do is actually assign you a seat.
If it’s a free for all and - as you likely correctly say - they don’t oversell the number of tickets against the number of seats, then the reservation card of the ticket is a little pointless really.
Do you have a reference for this?
I’m not questioning that it happens - it’s a common thing in high volume hotels or high value airline routes after all - but I’d be interested in what sort of margins they oversell at.
That said, most of the documents would likely be commercially sensitive I should imagine.