I was reading an article in the Dec 15th copy of Ligonier Echo last night at mom's about a warrent served on a person.
I think it was for domestic, but that is not the point.
In the article they stated the sheriff department did not find all the weapons registered to the person and that the person showed them where the items were.

Are they allowed to have lists of what we have registered?????
I didn't think they collected this information.

Handguns --yes. one of the forms filled out for HG purchase in PA goes to the State Police and is kept IIRC ---in fact circumspect registration. I was under the impression (not sure where I heard it) that a lawsuit was pending in federal court to stop the practice and have the existing records destroyed.
hand guns purchased outside PA,prior to PA residence or without the benefit of a dealer transfer (and therfore illegal) would not be recorded however, for whatever thats worth. The couple of handguns I have aquired since moving to PA I was told by the dealers to keep the state form --not with the gun for some reason--always, even if I disposed of or transfered the firearm.
Also the subject of the warrant may have owned classIII firearms and therefore a registry would have existed for them.

These were the guys suing the PA State Police over the handgun resgistry.  Unfortunately, they have lost almost all of their cases and now I believe its going to federal appeals court (if it is going to go any further).  They used to have a link to the timeline of events in the case but I cannot find it on their webpage now.