Drone
I am well aware that both DS9 and Voyager referenced TNG, my point is that for the number of episodes they had, all three more then twice what TNG had, and in I think all three cases over 70 more then enterprise had. they have more material to reference, more time to make those references, and they are references events that could have taken place the same year to as much as 8 years after the time of TNG.
So factor out the differences in the amount of episodes that could be referenced, and the number of episodes they could be referenced, and factor in the difference between zero years to at most 14 I think, to that of over a hundred years.
i mean even better then comparing how many times TNG references TOS, since its less then a hundred years difference and the difference between ENT and TOS is over a hundred years,a t least internally by modern Trek productions reckoning. A better comparison would be how many times Deep Space referenced dos, and even better yet how many times Voyager referenced events from TOS.
now we do know that DS9 at the very least referenced events from TOS, with the characters of Kor, Koloth and Kang at least by using the existing names of characters created in toS in the same episodes those characters appeared. and certainly when dS( goes back in time to Trouble with tribbles references abound. but outside of those episodes that have direct connecting material of either characters or the cast interacting with those characters, How many times did dS9 reference TOS?
With Voyager outside of Laneway and Kim looking into the past events from Undiscovered country, still not part of any event from TOS, how often did voyager reference TOS. TOS which features the first use of a functional replica of a human in holographic form that its solid to the touch and capable of moving outside of a holodeck, might get some mention from the doctor you would think. heck while Voyager makes a couple references to tng facing the Borg, no mention either time of Picard successfully being disconnected (or even Lore for more Long term issues) from the collective, and how they would have crusher's references for surgically removing the borg tech and nano technology, considering they had to deal with that on more then one occasion.
Using voyager versus TOS is the closest time reference we would get to ENT to TOS. Then limit the references to say the first 100 episodes to see how many could be made.
Again the how point is that outside of events using the same race or characters Trek hasn't often referenced any similar type events, and the vast number of races that one series interacts with, especially over time, aren't mentioned again in later series. Even with modern Trek only a handful of major races get referenced between series. Typically species that are not based on one planets race, but races that have amassed many worlds. Though off course their are a handful of exceptions like the use of Bajor between TNG, DS9 and voyager. The possible reference of Tholia, we have no idea if they represent more then one star system (though in my mind it does, II don't think there is any true episode support to that, though I could be wrong).