If it is a Colt Vest Pocket model, 1921.
if it's a 380 caliber then made about 1924
Between 1921 and 1982, MAB made several pistol models in .25: model A vest pocket pistol model B vest pocket pistol model E pocket pistol model GZ pocket pistol (actually made under license by Spanish gunmaker Echasa, as MAB Espanola) The value will depend on which model it is, which version of that model, and condition. Since 2010, the range for the above pistols is about $50 - $300.
No more than 50-60 USD
Stevens was in business from 1864-1950. They did not have a "pocket pistol" model, but DID make a "pocket rifle" model from 1869-1916. Am aware of no specific production data based on serial numbers.
updated answer: The .380 Remington Arms UMC [Union Metallic Cartridge Co] pistol is the semi-automatic centerfire model 51 pocket pistol, also made in .32 in much smaller numbers, with production of the two calibers totaling about 65,000 from 1918 - 1927. The model 51 was designed by famed weapons designer John Pedersen, and all model 51 s/n start with "PA" for "Pedersen Automatic". They are highly regarded for their ease of use (although not ease of disassembling and reassembling). Primary US competitors were the Savage Arms pocket pistols (models 1907, 1915 and 1917), made 1908-1928, also in .32 and .380, and the Colt pocket pistols. original answer: Pistol? Semi-auto Model 51. No pistols.
what model pistol ????
gunpartscorp has pins for the pocket model, but not the self loader model. See their website.
That question can't be answered. In order to value a pistol, you have to know the make, model, possibly the age, and exact condition.
100-1000 depending on EXACTLY what you have and its condition.
100-400 USD
Impossible to answer without knowing name of manufacturer.