What I have observed is:
If the lens comes in a cardboard box it will have both front and rear caps.
If the lens comes in a screw in "jewel" case, it probably only has the front cap, as the rear is screwed into the jewel case. Then it is up to the buyer to buy a rear cap, if he wants one.

And all bets are off for used lenses.
Caps could be added or removed/lost.

If the lens is kept on the enlarger, there is a good chance that the caps will be lost.