Generally that works but sometimes it doesn't.

For example, some people say statements like "I don't want no towels".

What they really meant: "I don't want towels"

What I get if I cancel the negatives: "I do want towels"

The meaning flipped :)

Double-negatives in the "not+no" formulation tend to be a special case. The easiest rule (as you realized) would be "If there's a 'no' before the noun (direct object?), in an already negated phrase, then ignore the 'no'".

It's technically incorrect but common English.

> That is incorrect usage though

We don't need no education

You wouldn't be here quoting that line if it were correct.

But pointing out that language rules aren't something that people strictly adhere to, with rigorous logic, is a useful observation.

Undoubtedly, but it was a response to someone explaining how to use English (correctly), not how to understand someone else using English (possibly incorrectly).

If I say 'proper nouns have a capital first letter' I don't think 'actually oliver sometimes people don't do that' is helpful.