I am not asking what size wheel, but whats the OEM wheel as far as design
odds that comes down to what the dealer who originally ordered the machine asked for/what tier wheel package , and or what the customer who may have ordered it wanted!
the main reason you have miss matched wheels now, is , odds are over the yrs, someone replaced tires and wheels, , due to being worn and or wheels being rusty, or, someone used some sort of fix a flat type sealant and found out, no tire shops want to deal with wheels that have that in them, and as such, just replaced the wheels!/tires~!)
as for if they got wheels with stem protection, most likely came down to, price, what the shop had or sells most of(to keep prices down)
or, , pending what type of work machine is used for, ,some may what them, , or not! , But IMO< odds are it just comes down to price at time of buying tires!
I would also guess that at some point in this machines life, t someone bought a a set, or maybe just two tire wheels with them, and then, someone again, as times passed and need for tires again, , maybe replaced ONLY two tires/wheels at some other point
thus, you now have wheels that are not all alike
its honestly not a big deal, and I seen many many machines like this
unless your working in a lot of debris that causes stems to get damaged, there really isn;t any advantage to having stem protectors,
if anything, I have found some of them are a lot harder to get a air chuck onto them, making it harder to be able to fill tires with air when needed!
SO< I doubt anyone can really tell you for 100% certainty what wheels your machine had when new, minus tire size!
if you really feel a need to have all matching wheels, I am sure BOBCAT will sell you a matching set and claim there OEM matching
they MIGHT also be able to pull your VIN and see what it was ordered with too!