Re: Typists using early PCs
Typewriters were originally big expensive mechanical beasts, so they wouldn't duplicate keys if they didn't have to. Hence the capital "O" was indeed used as zero, and the lower case "L" was used as one. Everyone learned to type using this standard, and so in future, all typewriters were built this way.
I'm not an expert, but I speculate that IBM's invention of the golfball typewriter was the start of including a 1 and 0 on the keyboard.
There is actually an Asimov short story which turns on the lower case L being read as a 1 - All in the way you read it in More Tales of the Black Widowers.