"Pinning" IS fruiting. The second stage of it, to be clear.
And you definitely want them out of the jars before they've formed pins.
I suspect that "pins" and "knots" (aka "primordia") are being used interchangeably in many of the replies in this thread. Knotting/forming primordia is the first stage of fruiting.
Both knots and pins are fragile, so birthing after either have formed risks damaging them and rendering them into aborts, forcing the cake to regrow new knots and pins.
When a substrate has shrunk inside a jar it means it's being consumed, so it's either been over-incubated or else got dried out too much, which would also inhibit fruiting/knot formation.
The best approach is doing a lot of grows and paying real close attention to everything whether they were successful or contaminated. Both are very educational, and eventually lead to mastering the process to the point where failure/contamination is the rare exception.
There's no substitute for hand's-on experience.