Has a bit of a "discussion" with a friend of mine regarding fire systems this week - and he brought up that Lemons had found a number fo systems where the gauge was stuck. Now he didn't say how they determined that - but it might behoove one to check.
I believe if you put the bottle in the freezer the gauge should dip nearly to the red, and if you then dunk it in warm water it should head for the green. If it doesn't move, then you can't rely on it.
I can only guess they pulled bottles out and found the gauge green but the bottle light - which would mean empty, because I can't imagine there being any gas left unless the leak had just started.
3M is phasing out NOVEC because they don't want to be associated with making PFAS anymore, but Safecraft says it will still be around in generic form for quite a while.