I can't find any reference to something like "combine the scores of new submissions of the same URL to the first submission's score" though. I guess that's either new information or incorrect.
I think that falls into the "noticed through observation" bucket. I'm relatively sure that it is correct, as I've noticed that behavior myself. But, I have no official standing here and I could be totally wrong. But that sure seems to be what happens in my experience.
That's absolutely possible. This particular pattern has seemed pretty consistent over the years, but unless somebody from the HN admin crew chimes in, I guess we'll never be 100% sure.
I think that falls into the "noticed through observation" bucket. I'm relatively sure that it is correct, as I've noticed that behavior myself. But, I have no official standing here and I could be totally wrong. But that sure seems to be what happens in my experience.