How to selectively delete unwanted messages in Gmail. Per this stack exchange: Exclude label from a Gmail search?
1. Get out of Conversation View.
2. Do a search with appropriate operators like:
before:2012/07/01 label:Delete-Me !label:Financial !label:College !label:Registration !label:Employment !label:Receipts !label:important !label:inbox
3. Next to the checkbox, select the down arrow's “All”
4. Select the new link “Select all messages that match this search.”
5. Click the trash can, and confirm the bulk action.