The deck belt broke on my recently acquired G5200. No problem I thought. Searched a few threads found a gates cross reference part # and bought the belt also bought the two front drive belts figuring I'd replace them all and start out with new. The deck is a RC48-G. Multiple threads suggested a gates 6845 belt. This belt was too long, it was long enough the tensioner allowed the belt to rub itself just to take up slack. A 2" shorter belt was required. Same situation on the deck drive belts 6831 was recommended, 6829 worked. Is it possible PO changed pulleys, or is there that much manufacturing variation in belts?
I don't know the specific belt number you mention. The type of reinforcement cord in the belt is very important for durability.
My example would be a Gates belt for a 72" landpride mower deck.
A Gates B158 fits fine. It is 158" long measured on the inside of the belt or 161" measure around the outside.
A Gates BP158 is exactly the same dimensions but is one of their Predator series of belts with a much higher strength reinforcement made of Kevlar. Its Gates part number is: 9186-0158.
The B or BP number of the belts is one other manufactures use so a Dayco supplier can use the BP158 and provide you with the same belt.
The other numbers are more for internal stock keeping and costing and are not much help when seeking an alternative.
I do not believe equipment manufacturers make their own belts. If they need a large enough quantity, belt manufacturers will build one to the equipment manufacturers spec. Fine for a $200,000 Mercedes, likely the tractor manufacture is happy with a stock belt for cost reasons.
Dave M7040