A tale of confusing tickets and receipts...

The other day I had to get an extension to my Z1-4 season ticket, on the
student discount, in order to go to Epsom. At Waterloo I presented my
Oyster, the paper receipt and my Young Person's Railcard as usual (although
the SWT staff haven't always ben consistent about whether I can get a YPR
discount for this or not). The SWT staffer was the first one to use an
Oyster reader for my card in such circumstances, rather than just looking at
the receipt. He said that my receipt had been printed on a Gold Card slip
and should have been printed on another, and that technically when in the
past I've been given extensions marked as for Gold Card I've been
effectively travelling illegally as I don't have such a one. Looking at some
of the past paper tickets it seems that one of the reasons I haven't always
got the YPR discount has been because of the Gold Card.

Does anyone know:
a) If/how I can get a new paper receipt for my season ticket for future use?
b) Whether it's possible to complain about the TfL staffer at Colindale who
created the mess in the first place?
c) If anyone TOC has ever considered selling extensions from ticket
machines, thus allowing the customer to buy what they know they need/have
the discount for? (And with Oyster surely it would be easy to validate
existing tickets.)