Yes - the parts for G5200 may be S/N specific based on manufacture-date.... HOWEVER, I have found that nearly EVERY part I ever needed has been superceeded several times over the years and many end up at the same replacement-part anyway.
I have used the Kubota online parts lookup for MANY parts and see the S/N based replacements for some of them... but following the superceeding for each of them often leads to the same PN
I guess I am saying that, based on WHICH part you are looking for, it may not make much difference anyway.
Some areas of the tractor were totally redesigned and NEED the proper replacment parts (or an entire assembly) For example, the steering-gear on the early models was too weak for the weight of the tractor and wore out quickly.... In such a case, you would be better off replacing to ALL the newer-style gears anyway.
My tractor has about 1/2 turn of 'slop' in the steering-wheel because of this early design flaw. Someday, I might pull it apart and machine stronger gears or press in brass pivot-points.