The Merlin brand was established by the Merlin brothers in 1918 but unfortunately fell on hard times by 1955 and was purchased by JRJ Cycles which later became more commonly known as Bob Jackson Cycles.  A subset of bikes with the Merlin badge were produced by JRJ as late as 1987.  This particular frame was located in NOS condition in an Alameda California bike shop around 2000 and eventually built up with Campy NR/SR parts and Normandy hubs.  The exact year is unclear as the number stamped on the bottom bracket can't easily be traced but likely this is around 1972 or so.  Bike is potentially for sale to a good home.