why does dashboard membership number not match list of members?
The dashboard is programmed to show memberships that have a start date, whereas the search is not including that filter. If you are getting a different number in the search than in the dashboard, click on the Start date column to sort in descending order to find the record that is missing a start date - once you update that record, the numbers should be one and the same on the dashboard and on the search.

Hope this helps!

Editing to include screenshot regarding my last comment: