You kind of run into the problem of The Library in David Brin's Uplift series, which contains the sum total knowledge of all the sentient species in all of the Five Galaxies ... which then leads to the condition of "everything has been done and solved before" making it difficult to add new knowledge to the database. It's not impossible to "find something new" which has never been recorded before, but when you've got a Library that contains the knowledge output of millions of alien species gathered across billions of years ... most of the unknowns have already been examined and scrutinized by someone already.
You kinda sorta have the same thing going on with various tech levels in an interstellar setting. Worlds that are low tech level and are part of a broader interstellar polity KNOW that fusion power and starships and lasers and all kinds of "space magic" technology exists and works ... they just can't make and maintain it themselves. They can be consumers (and even scavengers) of high tech stuff, but not producers of it. The low tech worlds don't have the supply chain and industrial base to make the high tech widgets themselves ... but they can still import them and make use of them (and need to buy more of them when the previous purchase inevitably fails or breaks or otherwise needs replacing).
My point being that just because a world is low tech doesn't ipso facto mean that high tech is necessarily "unavailable" (because it can be imported) ... but that high tech will definitely be at the far end of a supply chain and will definitely be more challenging to support and keep operational (not impossible, but the parts and spares for maintenance and repairs will be more problematic). This is why I take the approach that building up your operations on a "locally sustainable" industrial and supply chain basis for your technology is the long term wiser choice, because it means that the "less capable" lower tech stuff is less likely to fail you at critical moments and will be easier/cheaper to repair and maintain. In other words, high tech gear in low tech settings is better thought of as being "disposable" because when it breaks, you probably can't fix it (locally) and will simply need to use a duplicate spare as a replacement (until that one breaks down too under usage).
To use a real world example ... just because a nation on Terra doesn't build its own cell phone devices, doesn't mean that cell phone hardware and service is unavailable. There are iPhones in use in countries that can't or don't build them, because the technology is imported ... but when those devices break or otherwise age out of service, the local in-country supply chain and industrial base can't fabricate a new iPhone locally, because they're not manufactured locally in-country ... the iPhones are imported. So in order to meet demand for the product, a supply chain network of imports from foreign sources has to be set up to supply the local market demand.
Same thing would happen (more or less) with technology differentials between worlds in a Traveller setting (it's just the scale that changes). Imported technology that is "higher" than what can be manufactured and produced locally can have a local demand but no local supply, in effect "forcing" an interstellar trade demand condition that merchant ships would then be "obliged" to meet (because there are profits to be made in doing so). Consequently, the higher the volume of interstellar trade a world engages in, the greater the opportunity for "anachrotech" to be in use and/or available on that particular low(er) tech world. Just don't expect those high tech items to be ubiquitous and in use everywhere by everyone (because, imports bottleneck in the supply chain).
And the merry-go-round just keeps on spinning ...
