I have a 3500psi Genesis 120cf tank with the skinny neck threads that was born in 2001. It is stamped with "spun" & "Japan". It's most recent hydro date is 2019. The test pressure is stamped into the tank. Apparently, it was possible to get a hydro done on them in 2019. I will likely retest the issue in about 4 years....Asashi cylinders were only imported by Genesis for a few years in the late 1980s and early 1990s. All pre-internet so I doubt you will find anything digital about their specifications. They were pretty heavy as I recall, in particular the bases were thicker than the comparable 3,500psi PSTs. Asashi cylinders had 7/8" necks and I am not sure their exemption is even valid anymore.
The Genesis 120 is the second most negatively buoyant tank I own. The only one more negative in my collection is a 3180psi Faber 108. My 3500psi Genesis 120 is slightly more negative than a 3442psi Faber 120. I am still looking for factory specs on the 3180psi Faber 108.