The difference is NOT B&M vs online, it's NOT pro/not pro, it's almost always a design/parts change or factory origin.
For example with any of the 44" tool chest 'system' every piece has at least 2 part #'s since they went to gloss red. They're up to 4 item #'s for the bottom, 2 for the others. Most have to do with which slides are used, as they're not compatible across each other unless the part # matches. They notch different holes in the box for the different slide retention mechanisms.
Ask me how I know. I have 2 tops, 3 bottoms, 1 7 drawer. Can't change the drawers in any of them except 2 bottoms that happen to be the same model #.