I think you're significantly underestimating how many words could be retokenized into multiple words even before considering how concatenation affects things.

I think you're significantly underestimating how many words could be retokenized into multiple words even before considering how concatenation affects things. For example: Concatenate is a word, but so are con, catenate, cat, and enate. Yes, no two of those are likely to be used in sequence, but I don't think that's a very reliable rule overall—"a" and "an" are both common words and negative prefixes.