That makes sense. I don't believe I have perfect pitch. Mine is more like "pitch the perfect" and depend on my tuner. That's when I get fussy. I believe that also explains why some of the notes that show up when I do a pull off sound a bit off. I only hear it in certain chords or songs. Probably just some 83 year old ears too.

With regard to your tuners vs. your dulcimers, remember that each tuner design uses a mathematical model when making pronouncements. Few, if any, tell you which temperament has been used. The ones with settings for chromatic-guitar-violin-etc. might not use the same model for all of them.

Tune until you are happy, and let the rest of the world roll by.

The question of A=440 or A=437, or Bb = whatever is a separate issue. Traditionally, "real orchestras and bands" tune by ear to whatever the oboe player sounds, not just sticking to some pitch fork or reed used before coming on stage. Having "perfect pitch" can be a real handicap.

"They aint' no perfect intonation" as most of my instruments staples are set by ear. (something close to  Pythagorean and sometimes called Diatonic Temperament) Each of your electronic tuners are off by a few cents just as each the temperaments are. Like Wally said the slight "off" gives the over all tone a wonderful depth. If it sounds good to you, it's all good. If memory serves me correctly, the folks on the other side of the pond have a sweet tooth for quarter mean tone? 

Wow! every time I think I'm making progress something new pops up. This is very interesting Wally. Let me see if I'm in the right thought pattern of this information. I have 5 dulcimers I have one tuned CGC so I can sing the music in the lower key. Two of my dulcimers are DAD. Even though the instruments are tuned differently (one C and One D) I would believe they should be the same bass on my cell phone tuner. They are very close but off enough if it were the same instrument I would tune to the correct note. My question is, does this fall into what you are discussing in the video? Oh! its ok if I'm "all wet" on this comment.  This may help too. The DAD is a Cedar Creek kit build and the other tear drop is homemade and tuned CGC. I'm what you may call "OCD" when it comes to cutting my fret boards and it shows up when I tune them. It just bothers me when I, for instance, tune the bass string one on D, Shouldn't it be as close when I use tuner on the "C" on my tear drop? If it were the same instrument going from one string to the other I would be correcting it on my tuner. Hope this makes sense. 

I just took another run through the linked video. 

If you primarily play in isolation, this may be something you want to consider. 

If you play with others, remember that they will probably be in different temperaments. In addition, using "pulls" and "slides" will change the temperaments. Others may be slightly out of tune by a few cents on one string. Using a electronic tuner for each string will give a different temperament than using the tuner on one and doing the others by ear.

As a former physics major, I find it interesting. When I'm a player, I use the tuner to set my bass string, then go by ear or trust the 4th fret.

I believe that the richness of an orchestral sound comes from the instruments being slightly out of phase and precise frequency.

If you want to re-fret one of your instruments, the spacing can be determined with 

https://www.thekimerers.net/brian/YAFCalc/YAFCalc.html

Equal temperamant. vs just intonation.

When I was surfing the web looking for different tunings I stumbled across this thought I would pass it on kind of interesting anyhow take care of everybody