I recently looked up DOM for my Police positive special on the Colt website. The gun has an "S" stamped under the serial number which I included in the search. The resulting search returned " No match ". Then I tried just the serial number and got a list of about five different models Manufactured on different dates (including mine; 1925). You don't say if you used a pre-fix or suffix in your search, but if you did, try again without it.
There are many, many members here more familiar with Colt than I am. One of them can doubtless supply better information.