That seems to be outside of what FGW▸ wish to deliver. Last year, when FGW overcharged ALL "First Class Eastbound Only" passengers by several hundred pounds, I asked FGW to write to those affected passengers. They refused and said that they don't have records of who would have been affected, and that customers would have to work it out by themselves. I also asked for a sandwich board/poster at the stations affected. They refused.
Being highly cynical I'm not sure I believe that at all (The part I've highlighted in bold).
Recently my Bank wrote to me regarding an account I held in 2009 which I have long since closed. Long story short, they had levied charges on my account which were not the correct amount and were refunding them in full with interest and a cheque was included in the letter.
Had the bank not have written to me, back then being a slightly naive teenager I never spotted it and wouldn't have known.
So actually, I think FGW are being extremely economical with the truth. Oh and once every 3 years I get a reminder to renew my Disabled Railcard...