It looks pretty good other than it there is no bushing on the Umnumzaan, the blade pivots solely on the OD of the pivot where it passes through the handle, not on a bushing which rides on a pivot.
Changes I know of, though I have no idea if timeline, are as follows.
Beveled the lock bar to make it easier to open a right handed model with your left hand.
Lowered the cut out on the non lock bar side to make closing the knife easier, it's often said that the lock bar was raised but that is incorrect.
Chamfer of the edge of the scales is different on all 3 of mine regarding the area around the lock bar and the choil of the non lock bar side.
The Idaho made stamp.
The new style of jimping.
The new pivot.
The lock over travel stop.
There were no obvious "hard changes" to the design, no single point of change for any of these variations as far as I can tell.
As an example if this, my friend (Blackend here on the forum) and I received 2 of the last 5 StarTacs to ever leave the factory with the original pivot, his showed up sans the over travel stop, mine had it. The ots was approx a year into production at that point. Both had the new style jimping and were identical in every other way.
As any good company does I believe that they use any parts on hand and must've found that scale in a box somewhere long after so many requests were made for a non ots knife we're made when the ots was introduced.
Blackend also received one of the first 30 25's a few weeks before I obtained one, his had what must've been a leftover prototype scale on one side as the lanyard cut out was completely different than the opposite side and completely different from my 25 from the first 30 knives.
I've also read posts where left hand Tanto Umnum's showed up long after the ots was standard that did not have it.
Waste not want not, good business and it makes for special collectors pieces if you notice the differences.
A true timeline would be a very nice piece of information but I doubt even CRK could provide one at this point with so many incremental changes.
No matter, its an outstanding knife in any configuration-especially the Tanto.
but this question has been run down fully in at least a couple of threads over the last 12-18 months - search will turn them up.