I think that most of the time even in exhibitions they stopped at the end of the game -- the pro had limited time and only occasionally went for a record. The longest exhibition run I've seen in person was Pete Margo's 198 (June 1980, Brewster, NY) which ended on a horrible scratch (imagine that!) and I think he would have continued for as many as possible but I think he had unlimited time and he was there as a favor to the owner.
I would add Eufemia to Cranfield and Schmidt.
Here is a fun story of how one exhibition ended at the end of announced length. The original poster is taking a vacation so I hope he doesn't mind if I repost....
CARAS RUNS 100
It was a bitter cold, windy night in Ithaca, New York in the fall of 1948. At the Student Union in Cornell University a crowd of about 60 students and a few faculty had gathered in a large room containing a dozen pool tables to see an exhibition by Jimmy Caras. A freezing Canadian winter wind was hurtling down Lake Cayuga and across the campus as Jimmy arrived with his “manager,” both wearing heavy coats, scarfs, gloves, hats – the works.
The manager made the following startling announcement in a loud voice: “Mr. Caras will now run 100 balls.” You could hear a distinct murmur spread across the room. Meanwhile Jimmy has removed his coat and is screwing his cue together, still not saying a word. I figured that he just didn’t speak English which is why the manager had made that announcement. A hush then descended on the crowd.
I don’t think the whole thing took more than 15 minutes. He never took a practice shot – just broke the balls and started running. The manager counted off the score and announced the next ball to be pocketed, as they used to do in tournaments. When Caras hit 100 the whole place burst into wild applause. He bowed to the crowd, unscrewed the cue, put it into its case and disappeared into the night, again without saying a word. A really amazing moment for all of us neophytes who had never seen anything like it.
John White