It's very common that when an engine gets a thrust upgrade, all future build engines (and engine hardware) get any necessary improvements to handle the higher thrust loads - that becomes the new 'standard'. There will be an associated Service Bulletin to upgrade any older engines and engine hardware to the new standard - incorporation of said S/Bs is a prerequisite to using the higher thrust rating on any older engines.
Since the differences between the two reversers appears minor, I suspect one is the older mark that doesn't have the higher thrust rating capability improvements incorporated.