For me the timeline looks something like this for Bolton's Rangers: (Before someone nitpicks this apart, I see these more as generalizations, some of the very specific I provided were more of a general idea of what this could look like, just trying to paint a picture with details, but the details could certainly be revised further)
The Years 2nd SW- 3040 "We have some tech manuals, they speak of things we don't really know how to build. If we got our hands on a LB-X autocannon through battlefield salvage, or lostech find, they might help us understand how to maintain it. But I don't think we'd dare employ it in combat, it's too rare, too precious. The actual battlefield contribution it would make is such a drop in the bucket to what it represents if we are able to preserve it, as we have preserved our tech library. Others might greedily expend their lostech in combat, but not us. This is part of our history, not combat equipment. We'd put it in the unit's museum, or perhaps on a parade ground-only machine, as one of our Star League relics, where it can awe and inspire and continue to contribute to the unit's mystique regarding its SLDF history. Every now and then we pull out a piece of equipment and put on a rare test exercise or test fire. To the "oohs" and "ahhs" of our honored guests. Many of our members are descendants of that history and so are very invested in keeping the unit's history alive."
The Year 3044ish- "Due to the Helm Memory Core the FWLM is starting to rediscover Lostech and put it back into production. Not just as relics, but as items we can actually manufacture and employ in combat and replace when lost. The 5th Brigade' tech library is contributing to that. Our techs and mechwarriors who have spent countless hours pouring over the library are working with the FWL's best engineers and scientists to contribute what we know to this effort. Initially those scientists treated us like bone-heads who would be useless, but we proved them wrong quickly. We feel like this is a race, all the Great Houses are doing this, and this tech library is our way to contribute to winning that technology race."
The Year 3048ish- "The tech library has made several valuable contributions to the FWL's efforts to rediscover Star League technology. Several manufacturing lines have been retooled to manufacture advanced technology variants. What was "lostech" is about to become just "tech" that we use everyday. Bolton's Rangers are proud of our contribution to that. Even if a lot of it will remain classified for now. The techs of Bolton's Rangers have also learned from them as well, putting us ahead of most FWLM regiments on actually having the expertise to employ and repair such technology in the field. We have several prototype machines, like our new -3M Goliaths, that we have actually employed in combat. Within the FWLM that makes us rare, only a few of the best-equipped regiments have such equipment and the qualified techs and mechwarriors to use them. Most regiments are having to wait in line, but Bolton's Rangers are on the cutting edge because of our existing expertise and contributions to this technological renaissance."
If you can't tell by the way I framed that, I see this less like the 5th Brigade having a lot of lostech and employing it in combat, and more that the unit may have contributed to the FWL's technological renaissance in the 3040s. But then ultimately the unit saw benefits from that, employing some of that equipment when it would be extremely rare and otherwise only found in a handful of Grade "A" units. Or maybe even slightly ahead of those units, if the 5th Brigade was tasked to field test some prototypes they helped to develop before they went into mass production.
To me, a really good story about this that would fit well with what we know from canon sources, would be a collection of Bolton's Rangers techs and mechwarriors getting pulled away from the regiment in the 3040s to contribute to some hidden super-secret tech renaissance project. Them arriving to discover some incredible covert effort to solve the mysteries of Level 2 tech. There are problems that the FWL scientists and engineers have been unable to crack. With their detailed knowledge and understanding of the tech manuals, the Ranger techs and mechwarriors are able to help solve some of the toughest mysteries and problems the FWL engineers are struggling with. Interesting story ensues.
Maybe toward the end of that effort some of those techs/mechwarriors return to the regiment, with some prototype equipment that the project wants to see tested in actual combat. (According to FM: FWL the unit was using some prototype -3M Goliaths in 3047, that could be treated as one for-instance of this kind of field testing)
EDIT: According to TRO: 3050 (the Original, which includes the Goliath as an entry) notes that Corean Enterprises was still building a small number of Goliaths (the bigger producer, Brigadier Corporation on Oliver, had been lost by then). But that the Goliath with its 4 legs and good stability, proved to be an excellent test-bed platform for a large weapon, the Zeus Slingshot Gauss Rifle. The success of those tests led to the -3M Goliath entering mass production. I could see personnel from Bolton's Rangers being brought in to be part of the effort to develop the Zeus Slingshot, as well as the variant as a whole and then employing it as a test prototype in the field.
Going back to the beginning here, of the original poster's question about 3025. I think Bolton's Rangers represent a group of people interested in preserving Star League relics back in 3025. Compared to some other combat unit that might not care about preserving history and care more about how that lostech find can be exploited today to have an edge to win a battle. (and in turn, it's highly likely, eventually destroying that Lostech in battle)
