Whereas the actual ticket may bear evidence of when it was passed through the barriers...
Do any employers really insist on receiving physical copies of the tickets after travel and then use magnetic stripe readers to see if they can work out what time it went through a barrier? I find this very hard to believe.
Even if the headcode of the the train was written on the ticket, it may not be accurate! And even if it was, is the employer really going to look this information up? Again I find this very hard to believe.
Are you talking about compensation, rather than expense claims? If so, then it is perhaps
slightly more plausible a train company may resort to the above methods, but many of the same caveats apply and I still can't see they'd have the time, and I am yet to have any company insist that I send physical tickets. I also will take photographs of tickets before the journey is completed to avoid potential issues with barriers swallowing tickets, or simply losing the tickets. If train companies were to insist on physical tickets being posted, I'd argue they'd have to ensure ALL gatelines returned tickets and did NOT retain them. I can't see this happening at all!