Here is a quick question that may go with this time period - Is there a canon reason that armor shifted from Clone Wars to OT Stormtrooper? Thanks!
I always thought it was rather dumb that the Phase I clone armor (esp the helmet) was influenced from Jango's, presumably as a visual cue (that we didn't need) that he begat the clones. The Phase II armor was better but seemed like an awkward, and rather hamfisted attempt to bridge the Phase Is with the OT TKs. I would've much rather seen GL go with some of McQuarrie's early TK armor concepts. They shared a resemblance to the OT troopers but looked a bit more raw and primitive. The evolution would've been more logical in my mind.
From what's out there, currently canon as well as on the EU side of the line -- but unlikely to be contradicted for reasons... The Phase I clone trooper armor is an updated and streamlined version of the Republic Trooper armor last seen in the Great Galactic War generations prior, back before the Republic disarmed. Mandalorians were active around the same period, but didn't have a unified "look", wearing whatever armor they could find, or had a preference for. One of the popular models had a T-visor similar to what the Republic Troopers' helmets had... And which was also reflected on other helmets of the day and in the period prior. It was apparently a popular design motif for armor manufacturers of the day. It has not yet been chronicled how that particular motif stuck with the Mandalorians and became part of their modern era look. But that the clone template was a Mandalorian was, honestly, incidental. Sifo-Dyas commissioned the army for the Republic. So the Kaminoans had their subsidiary contractors make Republic armor while they began looking for a suitable candidate.
As for the evolution of the look... There were a lot of issues with the Phase I helmet which showed up only in actual combat. Within a year or so of the Battle of Geonosis, they'd rolled out the Phase II helmet, plus a whole bunch of function-specific additional helmets. Following the Declaration of Empire, even though the Clone Wars were over, there was a lot of resistance to Imperial rule to put down, and scattered rogue Jedi to find and eliminate. So the newly-rechristened Stormtroopers saw their armor continue to develop. While The Force Unleashed's story is probably not applicable any more, I do consider a lot of the trappings to be valid, including the various armors we saw in there. Within a couple years of Order 66, the 'Troopers were wearing what I consider Phase III -- the helmet is more transitional between the Phase II Clone Trooper and the OT Stormtrooper, and the armor is mostly what we recognize as Stormtrooper, but still with Clone Wars era holdovers like separate elbow armor.
I can also see the Empire streamlining production. Two or three common cockpit modules for Imperial fighters that can be equipped with a variety of mission-specific wing panels and other gear, for instance. All the helmet and armor variants in the Phase II era (jumped from half a dozen or so for Phase I to more than twice that in Phase II) required specific manufacturing for all the unique pieces and components. Rogue One shows us that the light infantry we saw on Kashyyyk in ROTS have likely evolved into the Shoretroopers, and the armored-vehicle operators still have their own unique gear, despite the Stormtrooper pilots' gear now being much closer to the base infantry armor and helmet, as in the OT. Over the next few years, the armored-vehicle operators' gear will follow suit, as we saw in ESB. Not sure if the Scouts evolve from the Shoretroopers, or if they were following a separate parallel evolution from the Clone Wars era light infantry...
Now, as far as variations between one film's stormtrooper armor and another's... I need more context, that's going to have to wait til I read Catalyst and see the film. I don't know what the details are for the 'Troopers on Jedah or on Scarif. I
theorize, however, that what we see in ANH and ESB is the general-issue Stormtrooper armor, while what we see in Rogue One is some limited-issue elite variant. Special troops getting better kit. I postulate the tube slits are a new feature on this model and that, after use in the field, they find what soldiers for over a century can tell any engineer -- if you make a recess, dirt will get in it; if there are moving parts involved in there, they will jam. No exceptions. I harbor the notion that by the time of ROTJ, this model has evolved into the Stormtrooper armor we saw on Endor (these were the Emperor's best troops, after all). Slightly different shape to the helmets and shoulder bells, different arrangement of details on the abdominal plate, etc. And the tube stripes were back to being nonfunctional.
So all of that is what's driving the evolving look of Stormtrooper armor -- correcting design or manufacturing flaws, attempting to maximize trooper effectiveness, and attempting to minimize costs (within reason). After all, even with billions of eager volunteers, it takes time and resources to train a new Stormtrooper, and those cost money. Cheaper in many ways to work to keep those troopers alive. I know Stormtroopers and TIE Fighters
look awfully disposable in the films, but try to remove the Hero Shield filter -- these are the elite shock troops of the Empire, and they've been quite effective at sowing terror and maintaining order through a large chunk of space for years. The Rebellion was in a very precarious position pretty much from when it went public. So many things right around the time of Rogue One/ANH, if any one detail had gone differently, it would've been all over -- at least for a good long time to come.
--Jonah