Well I've been a SPA guy since 2004(I'm the only one left from the initial group). I don't load package cars or do the data acq part, but I can say that it makes the training of the Primary sorters much easier, they just need to know how to read and be able to match the color on the label with the color on the belt.
Out of all of the SPA guys in the aisle right now I was the only one who received actual training in it, now the new guys are just handed the gun and told, "Scan that bar code, stick the label", and they don't do the job so well.
As for the wrong labels on the packages, it happens. I personally don't get many(maybe 1-2 a month) many of the newer guys seem to get them alot. Especially when they're just starting out(One guy had 56 in one day during his first week!!)
I try to help them out as much as possible, but I can't watch them constantly, I have my own job to do.
Another thing is the packages that weren't delivered because of bad barcodes. We get them back in the local truck during the preload, and they have to be reSPA'ed, sometimes the old labels aren't crossed out, sometime the barcode is messed up and data acq isn't smart enough to put a new one on, sometimes they're NIB that have been floating around for weeks.
Sorry for the rant from a SPA guy's perspective.
Basically what needs to happen is to FULLY train everyone involved in the PAS, make sure data acq, and SPA guys know how to do their job and do it properly.