Lastly, I bought some of those 'close-out' low priced belts from Rock Auto Parts for temporary spare belts because I couldn't afford to buy expensive spare belts at the time. I want to mention that some of these 'close out' belts could be quite old, or they could be fairly new. If they are quite old, they probably won't last as long as a newer belt would, simply due to ageing of the rubber. That's why I am considering them as temporary low cost replacements.
The recommended replacement interval for V belts is 3-4 years. My PS belt is probably 25-34 years old. Yes it could snap any time, I just didn't have another to put on when the ALT belt went. If it holds up another 55 miles I'll be happy. That's as far as I need to go to pick up the batch of belts I orders and had sent to a post office in a town where I'll be for a few days next week. Then I'll spend the couple hours needed to pull all the belts again and put in the all new "closeout" belts: Fleetrunner for ALT, XLs for PS & AC, and the OReilly one I bought back in Feb for VP.
The 3-4 years is under extreme heat and pressures from being under tension and being run. I doubt belts sitting in on a warehouse shelf are going to degrade enough that they can't be used for 3-4 years. It's not like tires mounted on a car that sit out in the hot sun with thousands of pounds of weight on them.
I have a lot more time and a lot less money to spend on this stuff. $1.50-$2.50 Gates XL belt on closeout vs $15 from WM/Amz is a big difference. My miles per year are pretty low, especially this year when I have been recovering from buying the motorhome money wise. (Buying tires and other vital parts).
By the time January 25 comes around (a year from the date I bought it) I will have put about 4,000 miles (give or take) so this first year has been ultra low. Next year, I intend to drive a lot more since my finances will be in far better shape after April or so and I can afford more miles.