This is a bug. I've tagged your question accordingly.
total, in the wrapper object, should always be the length of the
items array, after concatenating all pages of results.
When I run /2.2/notifications?pagesize=100&filter=!*L6X1NqVdlFobvlv, I get 4 pages of results, currently totaling 382 items:
total remains fixed at 77. This is clearly a bug,
total should be 382 in my case.