I have several of these guns and learned a lot about them while trying to get my first one. The 4 inch model 66 that you bought was not a true "commemorative". What happened was in the late 70's they went from blued guns to stainless guns. During that transition the troopers were given the opportunity to purchase one for themselves. The ones that have ISP ### are guns that were purchased by a trooper.
The true commemorative gun is the 6" model from 1983 that came in the wood case. It is the 50th anniversary. All of these guns show 1 of 1117, as there were 1117 of them ordered. I have seen many people list these for sale at an outragous price thinking they have the first one. All of them were marked this way.

In 2008 ISP had its 75th year anniversary and offered a Glock .45. There were only a little over 100 of them ordered so they are a lot more rare. They are marked in gold showing the 7th anniversary.

If you have a 4 inch stainless model 66 with the ISP badge on it and no other special marks (like the ISP###mentioned above) then this would be a gun that a trooper carried.
As far as value goes I have spoke with many people and have been told that their true "book value" is the same as the gun would be without the marks. I have purchased the model 66 4 inch issued guns for between $200-$300. These usually show a lot of wear as they were carried for a long time.

The 50th anniversary 6 inch guns typically sell for about $500.00. What you will find in dealing with these guns is that a trooper or retiree hold them at a higher value then what a gun shop would have them at. I have two of them and have been offered $750.00 each for them by troopers.

I tried to find a 4inch model 66 (ISP gun)for about 2 years and couldn't get one. Then within about a 3 month period I bought 2 four inchers and 2 of the 50th anniversary 6 inchers and put them back for my kids.
So if you decide that you want to sell them talk to a trooper or go to an ISP post and see if anybody wants them, you will get a lot better money from them then just selling to a gun shop or listing them locally.