The immediately subsequent edition appoints a referee, so your doubt with Traveller might not be an example of incompleteness according to your definition.
5e is complete by your definition. Basic Rules appoint a referee so perhaps that covers it.
There's a sense here of a Goldilocks standard for having everything necessary and appropriate. Too many such guidelines would be cumbersome. You're identifying the Basic rules as having too few. I don't mean this pejoratively.
I see this as a question of ELEGANCE OF DESIGN. As an engineer, I have a deep appreciation for this trait in things generally. The PbtA core RPG design pattern is extremely parsimonious and super elegant. It handles ALL questions of authority, the regulation of who speaks next and what they can say, etc. in a very concise and well-described set of simple rules. D&D OTOH, in all editions, does not have this characteristic! It exists as a mass of specific rules, which sometimes have been kind of almost post-hoc generalized into things like d20-based checks and such. I mean, sure, 5e (and previous WotC D&Ds) were built with this concept in mind at the start, but they have NEVER really cleanly and clearly articulated a single unified "all actions flow through this loop without need of exceptions" process such as that which every PbtA is built on.
It is interesting to look at the history of criticism and analysis of these two different game families, and their evolution over time (albeit that D&D has a much longer history, etc.). People argue about PbtA games in terms of the quality of the moves provided, the coherency of playbooks, and questions surrounding the quality and thematic appropriateness of 'supporting rules' (IE harm, equipment, money, situation generation, etc.). There have been ELABORATIONS made on the core 'move loop', such as with 'FitD' games, which are clearly related to PbtAs, but have elaborated move processing in various ways. The basic ideas behind PbtA seem pretty uncontroversial however in terms of their applicability and appropriateness, or structure.
D&D OTOH is still arguing about core systems design! While every iteration of D&D has certainly carried forward many of the 'traits' of the original game, there is little similarity at this point between 5e and original D&D in a rules sense. There seems to be little agreement as to even what are the important principles and concepts that make a game D&D! And this started right at the earliest days, when Jim Ward developed the Metamorphosis Alpha game, which is clearly based on D&D. Yet it discards major parts of the D&D rules, and uses a lot of the rest in a very different way. I think you would be hard pressed to find a PbtA as divergent from AW as MA is from D&D, especially when you consider that the tone and much of the sorts of action are not really that different between MA and D&D!