Gmail Filters – Using Parentheses to Group AND/OR Operators

1. Use labels/filters to tag the emails from the ones you want to keep.
2. Use the filter to Archive the emails with those labels.
3. Everything else remaining in the inbox can be assigned to a new label called "deleteme"
4. archive everything with that label

At this point there should be nothing in the inbox. Of course all the emails still exist, the archive function just removes inbox label.

If you are running out of space, then go to the label "deleteme", select all the messages, and click the delete button.

Did you validate the actual numbers? The count of results is an estimate, indicated by the word "about". In the version of Gmail I see today, for a search like your first one, I get:

1 to 20 of about 192

But when I page through the results clicking the > button, the counts change:

21 to 40 of many ... 41 to 60 of many ... 61 to 80 of about 172 ...

If I keep paging through, I arrive at the precise number:

221-238 of 238

It seems logical to me that combining another search with OR might give a lower number than both separately, since they're estimates.

Another explanation assuming result numbers are precise: the search hits are on message threads. It's possible that a thread can contain messages from:user1@example.com AND from:user2@example.com -- can you check that angle?