Playing a game blindfolded seems like incredible feat if you are not serious/competitive chess player. Playing several sounds like magic. The thing is though that at certain level almost anybody can play decent blindfolded game, especially vs much weaker opponent. Playing several takes some practice but it's mainly connected with not being confused (anchoring positions to something so it's easy to switch). It's really not that much more taxing on the brain as chess players have tons of positions memorized anyway. I am talking about 2-3-4 games. 10 is already very impressive to me and things like 20+ is insane even for competitive chess player standards.

I don't think about individual pieces placed in a board but rather interactions and moves. Pieces are not located at random, you can remember where pieces are because you remember the plans, the threats and the moves that lead to a setup. If I had to remember seemingly random arrangements of pieces it would be a completely different story and much harder.

Might help that I also played Shogi rather intensely and after being used to Shogi, the chess board feels very small.

When I'm alert, jacked up on caffeine, I can keep track of 100s of classes, 1000s of methods and member variables. When, I'm in the flow, I basically write the program in my head and let the fingers be my mouth.

There's a fair amount of new code... I'd say 10000 - 15000 lines, some of which I generated.