> I'm finding a few urls that weren't downloaded.
You should look in the log to find out why.
I always run with retry=9 timeout=30 to avoid intermittent network problems

> I'd like to submit just the few missing urls to
> httrack for download.  Is that a good approach?  Or
> should I just rerun the httrack using the original
> filelist?The default is to purge files not in the mirror. I'd stay with the
update.

> Will the lack of last-modified-date impact httrack's
> ability to cache / update the mirror?You're already using update -iC2 but
I'd guess it will redownload the files.