I've been working through a combined 'fact dump' made out of different fact dump posts on s/debatealtright,

Oh great, I'd be happy to have them added

Is there any way to submit multiple links

For a single source, "no" - but, you could put the additional links in the "Source Notes" section if you wanted to save them with the source. I would need to decouple the URLs and Sources in the database to accommodate multiple links for one source. It's probably a good idea to have those backups in the future, but the 1:1 Source:URL relationship is how I started out and it would take a significant amount of re-architecting to change that. Of course, you can change the URL for a source anytime if it breaks and you find a new one (or just report it as "broken").

I have about 20 entries which do not appear at all to have yet been added to AltBase. I have also found more links for a number of entries which have already been added.

Great. I'd say "add away" - but unfortunately right now the "sign-in" feature isn't working because of changes I had to make during the DDoS. I'm uploading a new version of the website soon (like, today or tomorrow, hopefully) with a few additional features and bug fixes, including that one. I'll let you know when that's done.