Why should we assume that Data
would "adapt to humans"?
I mean, what would his motivation for this be? A human might feel pressure to get socially accepted, to conform, to learn the ropes. Why would an android?
Data learns things when he gets the spontaneous urge to do so. He got all excited about sneezing in "Datalore", not before, not after. He attempted painting in "11001001", not before. There's no sign that he would have been making steady progress towards imitating humans perfectly - quite to the contrary, he could turn on a perfect imitation whenever he wanted (such as "In Theory"), but had no desire to leave the mimicry on for any length of time.
Data may aspire to be more human, but that never manifests as him trying to blend in. He always approaches his goal by being a curious android, in both senses of the word: he is inquisitive about the world around him, and he radiates strangeness, often because of his inquisitiveness. Sometimes strangeness is a tool he uses for learning more, even.
I don't buy the "Picard was the first one to care" argument. In order to reach the position on the Federation Flagship and the rank of LtCmdr, Data would already have to be a pet project or close friend of a number of influential people - in either case getting plenty of attention and exposure. Even hanging around with Commander Maddox would have exposed him to the facts of life. No, Data probably learned perfect human mimicry during his first year of awareness already, unless Soong had built it into him from the get-go.
Data isn't babylike because he's undeveloped. He's babylike because he's alien. Unlike an abnormal human such as an autist, he's alien not because he'd be incapable of being normal human, but because he's disinterested in settling for mere normal human when that's neither his natural state of existence nor the limit of his abilities.
He doesn't know about "snoop" and "eager beaver" (which is simple reference file data) but he DOES know about Joe DiMaggio, Joltin' Joe, the Yankee Clipper
and Buck Bokai of the London Kings. Right.
That feels very true. The things you list him as knowing about are facts one can easily assimilate today by googling the keywords - most of the hits will be relevant, as the items in question are simple facts, classic encyclopedia material. The things you list him as not knowing are related to the use of language, and an attempt to google them will yield very little solid data or grammatical or etymological advice - you'll mostly get garbage.
"Snoop" isn't something Data would have to face in everyday life. He'll get it if he's interested in it, but his interest is not systematical by a long shot. Yet "snoop" is a phenomenon to be comprehended, while Joe DiMaggio is a dull, context-free fact to be quoted.
Timo Saloniemi