The question underlying all of this is "What does Tech Level represent"
The intent of Tech Level was to be a quick guide to a Traveller (in a TAS datafile, for example) as to what he/she was typically likely to encounter and/or what they could likely expect to find if they went to that world. (This is from a game design viewpoint - the intent of the UWP string for the GM to hand to the player). As a result, a Traveller could certainly encounter an Air/Raft on a TL3 world if the world rulers and/or other wealthy bigwigs had imported some for themselves, or if the rulers intentionally maintained the world at low TL for their own purposes and restricted high TL for themselves, etc.
In general, the question you need to ponder is: How do you interpret the world with Population Code=2 and TL=13 (or TL=7, for that matter)? Does this small colony of less than 100 people produce their technology locally? If a research colony of 30 people uses TL12 equipment that is supplied from off-world, do you rate the colony as TL3 because that is the best they could hope to make themselves with their own personal skills should they get cut-off from the outside universe?