Does anyone know, or can anyone explain tube measurement numbers?
For example, one set of tubes has a “30” written by hand on the outside of the boxes, while another set of the same kind of tubes has the number “19” written by hand on the outside of the boxes.
That’s no good! 
Just kidding I have no clue. 
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I’ve tried to look it up and only get descriptors of different types of tubes, but haven’t found anything whether 30 is better than 19, or whether 19 is better than 30, or whether they are both good numbers, and what the difference means (for the same type of tube). Someone has to know.
I can only offer solid state as a solution to this dilemma. But you are correct someone here will have your answer.
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It might be just as simple as a reference the tester, or even the inventory person used for whatever reason. Going though 30 of these, 19 of those… whatever.
Plug 'em in and listen!
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Boo, lol
Depends to some degree on what tester was used. Most testers have a scale that, through the selection switches set for a given tube type, will cause the meter needle to hit the same number for what is considered “good”. On my B&K 707, the scale goes from 0-120 with “good” starting at 65 - although obviously if the needle reads higher the tube is “gooder”. 
There are some tubes, though, where minimum “good” might be a different number on the scale. It all depends on the tube tester’s settings ability to get the needle to swing full scale for a given tube type. Most tubes and testers work in this way. So without knowing the tube type and the tester used, it’s hard to say - although numbers that low are usually not great.
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Hopefully 30 is the best. Lol
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Without more of a context I’d be guessing, and suggest asking who ever sold them to you.
For example it could be gain (mu) or transconductance (gm) or plate resistance (Rp). Based on the numbers my guess is mu, and they should be tightly matched.
Assuming the numbers are mu, based on the magnitude it is likely: mu=30, would be a voltage gain of 30/29.54 dB. Likewise 19 would be a voltage gain of 19/25.57dB.
Knowing the actual tube type, manufacturer, and application would be helpful in providing a more meaningful answer.
My guess is you are referring to your new E88cc tubes, which are a dual triode voltage amplifier, and mu should be closely matched. Did you buy a matched pair?
Also, thet tube tester used, methodology, and tube burn-in/warm-up are all important. A number by itself is no more than just that.
Anyone interested in vacuum tube gear and specifically vacuum tubes should consider owning a copy of the RCA Receiving Tube Manual.
The tubes pictured above a part of my secret stash. I have never powered them up. I do recommend spare tubes and fuses for that day when….
Feel free to call me if you care to discuss further.
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I should add, considering the difference, I would NOT just plug them in until you know what they represent. Not likely any damage would occur, but the source is going to provide the best answer. If they can’t explain to your satisfaction send them back.
Too late, LOL. I plugged in the ones that measured “19”. They are quieter tubes, both in volume level and in quiet background. I had to turn the volume higher to have the same vocal bloom, and they are silent, without noise, close-up to the speakers. They do also seem to have a little less “magic”, but also have a pleasing tonal balance (less tubey, more clean). And yes, I am potentially quick to relay my first impressions, but this is what I hear.
I also have tubes from “National”. Mine are EL34’s that I have not tried yet.
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So are these NOS E88cc from the Tube Depot? IME NOS doesn’t always equate to sonic satisfaction. Especially NOS 1960’s JAN (Joint Army Navy) tubes, which tend to disappoint. Those “National” tubes are actually Japanese Matsushita’s. Possibly the best value oriented tubes I have had the pleasure of listening to. My tube preamps are known tube eaters, Audible Illusions. Great little preamp, but biased high, so NOS Mullards, Telefunkens, Siemens, and Amperex need not apply.
These days it is extremely difficult to get reasonably priced vintage tubes that are listenable. Most have been bought up many decades ago by tube-o-philes.
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I think I have most of the TFK ECC801s’es and Valvo 6201 Blue Labels that were being sold at the time. Plus some others.
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I have a stash of Ediswans and Tungsrams as well.
Now that I am getting out of tube gear I have to decide how best to disposition my tube stash
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My “National” tubes say made in China
Interesting , I wonder how that came about.
If you don’t mind my asking where did you get yours?
Directly from CJ
When the supplies of tubes from the US and the EU dried up they started buying bulk from China and rebranding them. All of my sets of 6DJ8 and 12AU7’s happened to be from Japan.
These are the ones I am referring to. Not familiar with a Chinese variant. The tube market continues to change significantly. IME Yugoslavian and Russian tubes tend to be worth seeking out. Regarding NOS the key is to finding a credible seller. Recently I have had good luck with Brent Jesse in Hoffman Estataes. For one, he stands behind his product. The down side is there are no bargains from Brent Jesse. I’d like to think cj would also be a reliable source, but am a little surprised they are offering Chinese tubes.
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Did you reach out to cj to determine the meaning/significance of the numbers?