Rear Diffs - question on 3 different types for 4.4L

[jbfrancis3]

I'm looking to purchase a rear diff from a 4.4L (3.64 ratio). I've found 3 different variations based on different part #'s. Not only that, but part #'s on Ebay differ by one digit from RealOEM!

Some posts on this forum cover nicely the pre-LCI (up to '03) vs LCI ('03+) rear diff differences. I.e. the medium vs vs the bigger case.

But within that pre-LCI run, there's another break point. '99-'00 have one part # and '01 -'03 have another part #. Here's a realoem breakdown using Feb as a test month in format of engine/prod month/part#:
M62 02/1999 1428652
M62 02/2000 1428652
M62 02/2001 7510654
M62 02/2002 7510654
M62 02/2003 7510654
N62 02/2003 7510658
N62 02/2004 7510658
etc.

What's the difference between 1428652 and 7510654? (Not the output flanges - I can tell from RealOEM that they're same diameter). Examples:
02/1999 (1428652): https://www.realoem.com/bmw/enUS/sho...diagId=33_1013
02/2001 (7510654): https://www.realoem.com/bmw/enUS/sho...diagId=33_1013

And THEN, why do used units on Ebay have 1428651 (not 1428652) and 7510653 (not 7510654), respectively, which is a minor difference on that last digit?

(1428651): https://www.ebay.com/itm/17526614859...3ABFBMjsmAhr5h

(7510653): https://www.ebay.com/itm/22493978056...3ABFBM8K297r1h

Thanks

[bmw540san]

Just a quick guess which may apply here:
Most of times ebay place will list part # they see on actual part while realoem will have the latest revision part listed. In a lot of cases it's the very same part. That can get confusing for a buyer.

[nick325xit 5spd]

Most likely the units were revised in minor ways. Sometimes that's an upgrade for reliability or function, sometimes it's just swapping out suppliers. eBay seller part numbers are also not dependable.