That might of been the ones issued out in 1861, about 25,000 of them. The other issue dates were 1863 (12,500) & 64 (37,500). According to THE RIFLED MUSKET by Claud E. Fuller. Great book brought it like 50 years ago for $4.95. It's on Amazon used for $18-45. Some guy selling brand new for $919. Gosh dang anyone know how to polish a book and make it look new?
Also in the book it states the only parts interchangeable with the Colt were Muskets made by Amoskeag Manufacturing Company or Lamson, Goodnow & Yale. Don't know if that includes barrels but if it does that might account for your 1862 barrel fitting well on that 1864 stock & lock. Now that I think of it all the pristine Colt muskets I've seen were dated 1864.