adverbs - "Each" in potential subject position in compound sentence always pronoun?

This question is related to: "Each" — pronoun or adverb

The sentence in that question is:

M and W are letters and each has 4 strokes

In that sentence, how do we know that “each” is a pronoun and thus requires “has” rather than “have”? With another adverb, it would be “have”: “M and W are letters and individually have 4 strokes.”

I'm specifically asking now about "each" in the following position:

[ (Subject 1 and Subject 2) (plural verb)], and [(each) (singular
verb?/plural verb?)]

“Each” can be a pronoun or an adverb. My question specifically relates to the position in a compound sentence where "each" could seemingly be either a pronoun or an adverb.

Bob and Bill each work in Boston.

Here, “each” is an adverb because the subject is “Bob and Bill.”

Bob and Bill work in Boston, and each goes fishing on weekends.

Here, how do we know that “each” is a pronoun, and thus requires a singular verb, as opposed to an adverb, which would continue with the plural verb? Is it impossible for it to be an adverb here?

In the sentence below, “individually” is in the same position as “each” above but is necessarily an adverb.

Bob and Bill work in Boston and individually go fishing on weekends.