There's atleast 15 variations of the double derringer. Some are true serial no's and others are batch numbers. You first have to clearly list the writing and it's location to even have a start on which type and model you have to get it into the correct period. If however if this is one of the last model/types (has the letters UMC on top of the barrel) and is made 1921 or later there is a date code stamped on the locking lug under the barrel. This code can be looked up on the Remington Society of America under the Manufactured Date link.
I don't see dbl in Remington, if you mean the dbl in general when when referring to a Remington firearm that's double as in double barrel shotgun, derringer, etc.
The value is determined by the series (date) and condition.
100-425 USD
The same year you shot your gradma you freak
100-500 USD depending on condition, accessories, box, manual, etc..
No known published sn data.
10-100 USD or so
100-450 USD
0-100 USD
No published sn data.
1937 assuming its not a hammer gun, if it is, then it was made in 1907
You need to give serial number.