On prop slippage -- pins do nothing but help you align the prop when you put it on. And neither do multiple prop bolts. The only thing that keeps
slippage from happening is tight bolts combined with correct advance.

I've run a Brison 6.4 twin for years with a single bolt hub -- no slippage whatsoever. I've run a DA-100 for years with three of the six bolts (I'm a weight freak)
with no problems. And a DA-50 with two of the four bolts.

Other than too much advance, the problem that causes slippage is compression. Usually compression of the prop. If you're running wood props, you must
re-tighten the prop bolt after the first 5 minutes of running (a very short flight!), then retighten it after each of the next two flights.

Another point of interest -- I've seen a six bolt hub used where all six bolts sheared at a high idle. They did so because they were loose. The bolts
themselves provide almost no torsional strength. It's through compression that they keep it all in one piece.

If you're confident that your prop was tight, look to too much advance as your culprit.