It is hard to write technically ungrammatical tp, since, with a few obvious exceptions, any string of tp words has a grammar and, indeed, often several. In particular, almost any two word string has several grammatical analyses: noun noun, noun adj, adj adverb, verb adverb,, and verb noun (the last is often a genuine case of ellipsis, as I think you are using it). And most of these structures with most words have a number of possible readings. In most cases, however, most grammatical structures and most readings a given structure are relatively implausible, and much more so when compared with possible common errors. So, while 'lili waso' can mean "avian small thing" (egg, nest, nestling, feather, etc.), it is much more unlikely to do so than to be a mistake for 'waso lili', a standard form for chick/ nestling. And the same can be said for the meaning "paucity of birds" or even "smallness of birds", certainly in a contextless discussion.
I don't know where you get your ideas about 'tan', but they are remote from tp. 'tan' is a preposition, "from, because" As a result it is derivatively a noun meaning "origin cause" and, though rarely used, a transitive verb meaning "expel", say. The idea that God created man as expressed by 'sewi li tan e jan' conflates these two notions somehow. The situation is not helped by the fact that the straightforward expression of "Go is the cause/origin of man" is 'sewi li tan jan', which also means"God is from man". The expulsion notion, God birthed man in some sorta physical sense, requires a prepositions object, say 'insa': 'sewi li tan insa e jan'. To be sure, objects get dropped ( understood), but doing so in this case is guaranteed to make the whole incomprehensible.
Even in the old days of 'ni li pi mi', 'ni li jo pi mi' would have been very weird, since it is hard ( though legal) to read 'jo' as a noun after 'li'.