For community care the Anchorage VA requires a signed letter on the Dr. stationary with letterhead along with all receipts, vouching that you made the appointment. This of course takes time, if the Dr . agrees to provide.
Then Depending on which person reviews the claim, they decide if they reject the claim, via regular mail, which takes three weeks and then reject supplemental claims stating you did not file within 30 days of the appointment. I suspect this is due to an end of year bonus received by the department head for saving money throughout the year.