I use several things to clue in on what year it was I did something or encountered a certain device.
(1) I associate my college and higher education year by year, and within a year by where I lived. (2) I associate my ownership or use of various sorts of typewriters with what year I still lived at home, or was in highschool, or in college, and whether or not I was the editor of my dormitory newspaper. (3) I relate each year of my employment with its reference to specific college courses (which I can check on my computer ~ everyone should keep a copy). There were 3 different graduate programs BTW, over a period of years, with marriage mixed in, and employment.
Before posting a specific date for the appearance of a particular type of equipment, e.g. Royal Typewriters, Underwood Typewriters, manual, electric, spacing electric, manual or auto return (yes there were both on manuals), first computer (IBM 360 ~ remember those?), first laptop, first this and that by year associated with counts based on when kids were born, house purchased, car driven, and so forth, I always find a respected technology time-line site to reference in case of dispute.
So, where did I make a mistake? I never put anything on the net that I have not BEFOREHAND validated on the net or in a book.
Go back to your first post on this matter and make the appropriate corrections then. Manual office non-portable non-electric typewriters were still being made in the 1960’s. Manual non-electric typewriters are still being made.