There's too many factors to make a judgement call to your question. If it was a common non-prefix variation with 80% blue, and compared to a NIB 20- Single-Six, then the NIB 20- gun is worth more.
To know an item is older does not necessarily mean its worth more.
But you can start by posting the barrel length on your gun, a partial serial number and its condition and if its boxed.
Chet15