International Reply Coupons -- Exchange

What was the accounting method for International Reply Coupons pre-bar coding? I assume that today with the bar code and serial number on the reverse of each IRC, that the Universal Postal Union is sent a computer generated file that allows each postal administration to account for their sales and that the physical coupons don't have to be sent to Switzerland. Is that correct for today?

If so, how was the accounting before that. For example, did each country collect all the exchanged coupons and sort them by country and actually physically send the coupons to Switzerland for credit?

Originally that is what they did. Alternatively, two countries could decide to settle up for each other's coupons between themselves.

What I have been puzzling over is how the Lausanne type coupons were processed. Previously each coupon would have the name of the country printed on them. But for the Lausanne type IRCs, that was optional, so they could not use that to determine who to charge for them. As near as I was able to determine, each Country was charged for the coupons sent to them, then given credit for the coupons they sent back to the UPU.

But were quite a number of coupons that were never exchanged. I can only imagine that countries got a rebate when the Lausanne coupons became invalid, based on the difference between the coupons sent to them and those they sent back in for redemption.