Oh, by filtering you mean to find which aren't added. Well, that'll be pretty easy assuming the pages are categorized together under a §comic:§ tag: add a search keyword like either of these:
NOT comic:COMIC NAME
You need to totally capitalize the §NOT§ word so it'll negate (otherwise it's considered a normal keyword and will just break the search), otherwise you can use the dash.
Replace §COMIC NAME§ with the name of the comic, case-insensitively. All keywords on Derpibooru are lowercase, so the system will just make the assumption and turn everything lowercase before proceeding.
Don't add dashes, underscores or any other characters to the §COMIC NAME§ unless the name actually has those.
Alternatively you can replace every non-letter and non-number character with an asterisk, §*§, so it'll do the hard part for you. For example if you were unsure if 'All In Good Fun' had any funny characters between the words and before and after the name you could do: §-comic:*All*In*Good*Fun*§
But if the pages aren't categorized together under the §comic:§ tag, you can only negate other keywords to narrow down it some.
Another way to help yourself a little is to use the reverse image search integrated to the site. It's not a perfect helper, but if the page is there, it -should- be able to find it.
Don't be afraid to ask me for help, I'll gladly be of assist