Simply reverse the process - you know the date portion so remove that then you have your record ID back?
So just have the user search by using the last 1, 2 or 3 digits instead of the whole number?
If so I wouldn't mind this but it would be simpler in my opinion on the user to be able to enter 11061511234 Instead of 11234 because it wouldn't require thinking. Or if they wanted to pull up all records within the 110615 range?