No they have never used a single deck (at least not in recent history). With some basic card counts - it doesn't matter how many decks there are - you are just trying to detect a Bias of 10s - not to know every card.
I gave up on blackjack a long time ago. I have played let it ride, but unless you "cheat" you do not have an advantage (even with the knowledge of your neighbors - I still don't think you do) and I played until I was up a bit and then left. My friend lost about $100 in 30 minutes and joined me at the poker tables. It is kind of fun, but only when winning
Liitle old ladies are my favorite at the poker tables
Then when they make mistakes - you make money. It cracks me up, because some of the men in their 50s and 60s get really ticked off at them when they make dumb plays - they don't seem to want to make money.
Some of those women have wads of hundreds - I think they are lonely - one actually lives at the trop (so she told me). Some of my best stories are of the old women playing poker. One was playing SOOOOO Bad that when the waitress didn't come back with her drink - I flagged her down when I saw her so the little old lady wouldn't leave. I guess I should feel bad