I just got a copy of Goforth's book, so I will answer on the date. According to the book, that gun was made in 1946. He says the numbers in that era are not certain, but it is the best information available. The "sealed" refers to the counter-bored chambers that recess the case heads and prevent any "blowout" from the rimfire cartridges from harming the shooter.
That practice started in an era when .22 high velocity cartridges were first being made; sometimes the case was not strong enough to hold the pressure, and the rim burst. S&W did the same on their .22 revolvers for many years.