There really is no way to write a computer program to check the number of entries and, based on that number, tell if a page is incomplete. For example, there may be 24 weather entries on 5 pages for a ship, and then suddenly, on 1 page, there are 12 for the morning and only 4 for the afternoon - that page would probably be kicked out as incomplete, but was in fact transcribed completely. There are multiple examples of more or fewer entries on log pages for just the weather alone that would just give any computer drive failure trying to figure everything out.
Hmm. But if that were completely true, then surely crowdsourcing wouldn't work at all?
The beauty of crowdsourcing is that the computer program doesn't need
to know the precise content of a page in order to assess whether it's "complete". Everything works by consensus. So if the large majority of transcribers agree that there are about 30 entries on a page, then a page that is submitted with significantly less entries could
be counted as "incomplete".
But I would guess there are no hard and fast rules as to whether it actually should
treated that way. Every project is different, and I've no doubt there are many diiferent variables that need to be juggled with in order to find the most effective all-round compromise.
However, that is not what I was getting at when I suggested that the current behaviour of the Finished Button might be "fragile". As others have pointed out (and I alluded to myself), it works just fine when people use it in the way that was intended. Potentially, though, it does seem open to abuse by a hypothetical malicious user who could just click through pages whilst transcribing little or nothing. But probably that possibility has already been thought of, and there are already measures in place to deal with it.