The US made tubes in the past had a harder vacuum than modern tubes, one of the reasons they lasted longer.
"Harder" and "Softer" vacuum was a marketing term invented by Aspen Pittman, Huckster, RIP. I believe he was trying to invent a term to reflect how much C voltage was required to bias the tube at idle, aka how much drive the tube would require to attain maximum amplifier output. 6L6 and 6550 types require greater voltage, EL34 and EL84 require substantially less. This has to do with the geometry of the tube innards, and not with vacuum depth inside the tube.
All vacuum tubes - audio ones, at least, are pumped down and sealed at around 10-6 millibar. A "getter" is then flashed, which absorbs any residual gas. That's the silver you see on the glass. If the vacuum was 'softer,' the getter would turn white, and the tube wouldn't work.
Old stock tubes made in the US, Europe, Japan lasted longer because they were made with premium materials with well maintained, fresh tooling in a competitive marketplace. None of that applies now.