(not giving legal advice here) Wait a second. You were stopped by an Illinois trooper with valid tags? What did he say was his PC?
Why I ask is because Illinois has a bad habit of targeting anything with Missouri tags. We hit Illinois from time to time and I've watched Troopers let Illinois tags fly by 20mph over the speed limit, but pull out for a Missouri tag going just 5mph over.
If the PC isn't there you MUST file a complaint with that Trooper's HQ as well as the ILAG. If it adds up like it sounds then it's another clear example of Illinois police-state tactics. Technically, no PC means you should not have to submit to any requests of the LEO on the stop as the stop is unlawful...ie under the color of law. One more reason to carry a recorder at all times!
If anyone travels to Illinois, know their gun laws for peaceable journey and follow them to the letter. Know that you have NO right to self defense in Illinois, you WILL go to jail. Also remember one very important case during vehicle stops: Grant v. Arizona. Absolutely DO NOT give any LEO in Illinois consent to search your vehicle.
Why? If they find a firearm, even in a locked case, they're going to press the matter and some have been known to say it's illegal for anyone to have a firearm in Illinois without the Illinios FOID card, which cannot be obtained by someone who is not a resident of Illinois. Personally, if an irresponsible Trooper unsnaps his holster I'm taking that as a threat and WILL be filing a complaint.
So what I'm gathering thus far is this: Unlawful stop by Trooper under the color of law (no PC present), runs your license through DOR to obtain some sort of evidence or to find out if you have a warrant under the color of law stop, finds out you have a CCW permit and communicates his heightened state of readiness (a threat) by unsnapping his holster, and begins to question you to the potential presence of a firearm in an attempt to gain evidence that you've committed some crime again under the color of law stop. If Illinois would have passed CCW, their troopers would likely know that a CCW permit requires a background check. Proves that they refuse to educate themselves to the kinds of issues that could save their own lives.