But no matter that your source is, the typing is essentially the same which brings us back to the acceptable error rate for a typical job.
I remember whiteout - I referred to it in my post. And I remember the correction tape where if you accidentally typed an "e", you would move back to it, insert the tape and hit "e" again, which would deposit white covering on the "e" and then you could go back again and type the correct letter.
But this all goes to my question. These are nowhere near as quick as hitting something wrong and digitally correcting it. A person with an effective speed digitally of 60 wpm, with error adjustment, would be much faster than the another person typing just as fast with the same number of errors, because of the time it takes to make corrections.
In my typing tests, even a tiny delay (hit wrong key, hit delete, hit correct key) will show an obvious reduction in typing speed in a one minute test. If I am doing 60 wpm, that's 300 characters. That's 9 errors in that one minute.
Now, doing it on a manual typewriter, I make a mistake and have two options:
Whiteout: apply the stuff, wait for it to dry, go back and type over it.
Tape: Go back to error, slide tape in, type same error to cover it up (sometimes had to do it more than once to really cover it), type correct letter.
All this takes many times longer. Think of how many letters I could type, if my speed is 60 wpm, in the time to just fix one error either of those ways.
Not sure, but I think eventually they made built in correction ribbons which would be much faster, but they didn't always have those.
So, it still seems to me there must have been some differences in how typists were evaluated, which MIGHT include:
They had to be more accurate than that we accept today.
The speeds were calculated differently - like not considering how long it would take to fix an error. So if you typed 60 wpm and made 9 errors, they simply counted it as 51 wpm with no consideration for how long it would actually take to correct (thus on the test you would never stop to correct an error as you go or at the end either).
A certain number of errors in documents was just accepted.
They used whiteout at the end and manually wrote in the correction even though it wouldn't look very good.
Whether they are typing from written text, a book, from their own thoughts, or anything else, I don't think that matters much.