I had customer with a White that his mower's ipl says the belt 1/2 x 60.5 belt but it requires a 1/2 x 59. I also a had a customer (now passed away) with a Yard Machine that also required the same thing.
I don't think anyone at MTD, other manufactures, or after-marketers knows what is what anymore. We sure make OEM manufactures look good when we fix mower from our experience with their goofs. If you want to see mess try looking a Husqvarna on Jack's; some are only partial IPLs.
For me I have nearly enough different size belts on hand now that I can figure what the screw ups are but still frustrating. I here lately spend more time researching belts than I do actual completed belt installations.
It like me being sent a supposedly 3/8 x 34.2 belt last year that actually was only 3/8 x 33.75 for a HU625HWT even the belt from Husqvarna didn't fit. I fitted a 3/8 x 34 after modified and moved the brake assembly to allow more swing of the engagement idler. The trimmer head still moved some when disengaged but have since worn in and is now stopping. I ended having to do the customer second trimmer the same way but it didn't take the half day I spent on the first one. It is the same that I had the replacement spindle shafts knurled to get the bearing to fit tight. The bearing were loose fitting which wore the spindle's journals until they were offset and out balance.