Good programming manuals that were delivered with the computers and with the compilers/interpreters have existed about for the entire time when MS-DOS was dominant, i.e. from the launch of IBM PC in 1981, which always had things like a commented BIOS listing, which was very instructive, and detailed documentation of all its hardware peripherals, until the mid nineties, i.e. until Windows 95.

Until the early nineties, the compilers and interpreters from companies like Borland and Microsoft came with big excellent programming manuals demonstrating how to use them.

Also any complex commercial application for MS-DOS, e.g. AutoCAD, Lotus 1-2-3, the BRIEF editor for programmers etc., would have voluminous manuals, including sections on how to write scripts in whatever embedded scripting language they were using.

Only for the users of pirated copies of MS-DOS, compilers etc., the access to manuals was more difficult and some of them may have even not been aware of what manuals were normally available for the legitimate owners. Most IBM PC clones also did not have much documentation delivered with them. Since they were made to be compatible with IBM, it was supposed that anyone who needs them will buy the original IBM manuals.

Since Windows 95, the vendors of hardware PC peripherals have stopped providing documentation for them, providing closed-source Windows device drivers instead, but before that, whenever I was buying some PC add-on card, it typically came with a manual providing enough information about control registers etc., that I was able to write an MS-DOS device driver myself, if necessary.