I have been playing pool for over fifty years with a slip stroke. I did ok for a guy who worked a 40 hr a week factory job plus overtime. I learned to play on slow cloth and dead rails compared to what I play on now. I also had a compound fracture of my grip hand. Whether that made any difference, I don't know. I did a lot of work with my hands. Sometimes I have a problem with gripping things too tight, so maybe it did.
I retired a year and a half ago and decided to improve my pool skills. I did away with the slip stroke, and what seems to work best for me now is to set my grip with all 4 fingers touching the cue, and when I get down to shoot use only the index and middle finger plus thumb of course. When I shoot off handed (left handed for me). I use 3 fingers and thumb, but that hand was never broke. The kicker is when I break and shoot a jump shot I use 3 fingers and thumb, and that seems to work best for me, but only for breaking and jumping. Again all of this may be because of the bad break I had of the bone just behind the knuckle of the index finger. I hope this helps explain. Any ideas would be apreciated.