Tube measurement question...

I recently upgraded the 300b tubes in my Manley 300b pre-amp.  I was running the Shuguang 300b-z treasures and on the recommendation of a friend I decided to try the PSVANE ACME 300b.  As many have already reported, my results were similarly positive, with the PSVANE tubes providing more punch, better dynamics and generally an overall better listening experience.  My question is regarding the tube measurements.  And I think plate current in particular...which I believe is what they are measuring and notating on the outside of the boxes and designating as Ia = xx mA.  The box on my Shuguang tubes says 65 mA.  My PSVANES measure at 80 mA.  I guess I have several questions...first, what does it mean exactly?  Is it telling me what the tube is doing or is it describing a limit?  Then I guess I'm wondering if the PSVANES, measuring at 80 vs I believe their spec of 60 mA...is that good/bad/or a no care?  I'm sure there will be variance in all the tubes produced within a certain tolerance...just wondering at what point, if any, it starts to matter, and in what way...

Apologies if I'm not asking the question properly or if I've left out some other key data needed to respond.  Pretty new to tube rolling and since this caught my eye I thought I'd try and learn something...

Thanks..