A rough timeline of the changes to the base TIE models running roughly 5 decades of SW time.
T.I.E. Starfighter: originally planned for the Republic, this was supposedly the first Sienar design to use a new type of engine (there was a Prototype before this one, but not much is known about it, and it is unknown what designation it had). The laser cannons shared power with the engines from the same generator so firepower and maneuvering were affected during heavy dogfighting.
TIE Fighter: these were the same as what appeared in ANH, orange gun barrels, similar to Vader's custom TIE. These ships had a separate generator for the cannons and did not lose performance during heavy use (correcting an engineering flaw inherent in the original design). These guns fired very rapidly as seen in ANH.
TIE/ln: the 'line' fighter, these were seen in ESB and ROTJ. Gun barrels were simpler, resembling conventional cannons. The fire rate appears to be much less than the earlier model. This fighter was also used for the basis of a number of variants including /gt ground targeting, /rc recon and /fc fire control. The TIE Vanguard also represents a variant TIE/rc with altered wings and added antennae.
Other models included light duty and training ships with less capability in firepower and engine output.
TIE Interceptors represented an upgrade of the TIE/ln with more powerful generators and from 4 to 8 extra guns mounted on the wing tips/hubs, with some models also retaining the chin mounted weapons. Whether this design represents a separate model series or simply a different version of the TIE /ln is debatable.
The EU states surviving TIE models were upgraded or modified with added armor and shields following the destruction of the second Death Star, including further modifications to the TIE/ln and TIE Interceptor.
The TIE/fo seems to be a further mod/upgrade of the /ln model with larger chin guns, different engines, changes to the wing spars and wings, and added antenna. The Special Forces TIE is a further modification with added ventral turret, larger antenna/cannon?, room for a second crew member and rear view window, and reinforced wing spars. It is unknown if the First Order operates other variants or upgraded Interceptors.
All other TIE series craft are outside the scope of this post since they represent radical departures of design from the standard Fighter with the possible exception of the Defender, with standard wing spars attached to an extended tail on a standard cockpit and wings similar to the Interdeptor. The defender was not a full production fighter and the facilities producing that model were destroyed and never rebuilt following the death of the Emporer, so it is likely this model never saw later versions or updates. The Advanced line of TIEs seems to have introduced several innovations to the basic TIE Fighter line but that line of experimental ships likewise is outside the scope of this post.
So, other than correcting some engineering flaws and adding mission specific modifications the TIE Fighter seems to have changed little compared to real world fightercraft of the last 50 years, any innovations to the main line being mostly modest. Even the Interceptor is a relatively modest improvement over the Fighter, and it is possible the Interceptor was deemed too expensive or difficult to maintain to continue to upgrade or upkeep, or a shortage of capable pilots might have sidelined the Interceptor, although that seems unlikely given the vast resources and manpower of the Empire until the drastic loss of territory after Endor. It can be argued that with fewer pilots to fly fightercraft could have led to a program of improved training.
Anyway, what about y'all? Any opinions on the nature of TIE Fighters and the actual measure of their gradual improvements and/or modifications through the decades?