When it comes to doing subs for films, I'm pretty sure it's just a matter of style and preference of the guy doing them combined with making it easy to read. For the '97 SE they didn't put ellipsis on the continuing line like they did in '77 for example. It varies wildly on how it is done on DVD subs as well. I guess there is no rule.

There are people that have been upset by the four dot ellipsis in the A long time ago preface and IIRC the three dots in the crawls for being typographical incorrect. ;)