You are right, and I too have developed a better ear through the process. But for the sake of discussion, in an emergency, when everyone's tuner battery is dead, the back up tuners are dead, and no one has their phones with their tuner apps and nobody has their emergency tuning fork or pitch pipe with them, and there isn't a piano available, hypothetically everyone could just tune off of one person's A string, and everyone would be good to go. I'm not arguing with anyone. I use my tuner. I'm just talking. Nothing better to do I guess. Speaking of, does anyone use a pitch pipe anymore? I've been thinking of it just for fun.
Yup, that's what they did in the good old days. I wonder how they achieved consensus on whose "A" was correct? Majority rules?