At my casual part time job, I'm only required to do a check on a situation every 15 minutes. The rest of the time I can read, watch TV or whatever. I've been reading some old Mechanix Illustrated, Popular Science etc which I really enjoy. I read this letter in the tech section the other day. I had sure never heard of this before.
Yes it is possible, seen it on an old Landcruiser, which had vent lines going into distilled cap. On occasion one would get towed in with this.
Not sure about the vacuum advance story though. Some disb caps still have vent lines.