This begs the question of whether the TLs are relating to the technology advancement on earth (skill + knowledge) or just the skill part as the knowledge is (effectively) universally available.
Not to drift off the thread topic too far, but I would generally go with the latter (though this may be different for a world isolated from the outside Universe which is independently pursing tech innovation). There is no reason why a TL scale should be tied to the TL innovation history of Terra (other than as a handy rule-of thumb and general guide for Referees and Players).
Part of the purpose of a TL scale is to determine what is available to a Traveller on planet, whether produced natively or thru import. If they can build it on-world using the tech at their disposal, then they should at least be classified at that TL, presuming that their effective native production ability is not superseded by imported tech. If you are using T5's TL paradigm, then you need to take into consideration "Stage Effects" of the available tech (e.g. Experimental (Standard TL -3), Prototype (Standard TL -2), Early (Standard TL -1), Standard (= "mature"), etc. ) and assign the TL accordingly.