Non-stock rear axle question

I am having a mechanic replace my rear axles (2000 Limited) and the parts I ordered (Yukon axles that fit my vehicle) are not the same axles as what are currently installed. The axles that have an OEM part number of 4231135400, which appear to fit the 2001 Limited

Does anyone know why this would happen? For example, if this is a modification that other people have made, it is possible that the previous owner did this. But I'm curious why someone would do this mod

 

Are you sure it's not just overlap of model years? If the axle didn't change in 20 years, the same part will be listed for all of them. Or, it may be a part number superseded. Sometimes the manufacturer will do a new batch or run of parts and change the part number, even if the actual part didn't change.

ETA: I show that part as fitting 2000, 2001 and 2002 vehicles.

 

The axle I bought is shorter (by about a 1/4") than the axle that was on the vehicle. So maybe it's just a problem with the axle supplier I used. Sounds like it is the stock axle and I made a mistake ordering. Where do you see that the part fits the same? If you could link the resource you used I would appreciate it

 

This supplier, https://www.toyotapartsdeal.com/oem/toyota~shaft~rear~axle~lh~42311-35400.html shows it being the same 2000 - 2002.

This supplier, https://parts.longotoyota.com/oem-parts/toyota-axle-shaft-4231135400 shows 1996-2002 Toyota 4Runner - 4231135400

 

I tried buying that axle, 42311-35400, and it doesn't fit. I think I've IDed the part number as 42311-35280, from entering my VIN number on https://www.toyotapartsdeal.com, but the problem is this axle is discontinued. Does anyone have experience replacing this axle and found a way to buy one?