The first obvious mistake in the list is that google doesn't default to AND anymore since ages. A list of two terms will be some random combination of one of them, maybe both of them, and occasionally none (and no, this doesn't happen due to fetch/indexing lag or stemming or autocorrect).
To get true inclusive searches you need to quote the terms, individually. People keep pointing at verbatim search, but verbatim performs phrase search, which is not what you want in most of the cases.
DDG suffers from the same. I curse them both. I've used some js to quote individual terms before performing the search to get back useful searches for technical terms.
But really, the number of times I now get pages which do not contain the exact terms I'm looking for is subjectively increasing.