The NAO would like all of us to keep all our receipts for 6 years (it used to be 7 once upon a time) because that is the 'industry' standard. When JPA rolled out somebody made an arbitrary decision that we should keep our receipts for one year and wrote the JSP accordingly. The NAO threw a dizzy fit and after much negotiation settled on a compromise of 2 years. I can't recall exactly when this decision was made but it was more than 2 years ago and was widely briefed at the time, so there really is no excuse for not having the required paperwork available.
Moreover, the requirement to retain receipts and supporting paperwork for every claim has been briefed to death by unit and higher authority staffs since long before JPA went live. As the public purse continues to shrink, we will come under ever increasing scrutiny to ensure money we have claimed is rightfully ours and it is in our own interest to be able to prove it.
Yes, it's a pain, and I too believe the current system costs more money than it saves but it's unlikely to change anytime soon. The conversation VF had with his passenger has been had at every level over the last 4 years yet here we are.