[bena]

Someone could easily see that if you have an actual reimbursement system in place.

If it's based on the honor system, I could claim the train ticket, then claim a bus ticket and say that the ticket was for something else, you were mistaken. Then claim mileage and say the bus ticket wasn't that trip, you made a mistake. Again, just like the train ticket.

So, yes, the claim needs to be backed by proof of trip or by a deliberate action on your part saying that you are claiming this right here on this date for this trip.

[throwaway22032]

In your example you describe "something else". If there's "something else", then that "something else" is an allowable expense.

[bena]

Lies are not an allowable expense.