Huh, we used to type in BASIC programs from magazines back in the 1980s and I don’t ever recall seeing any kinds of checksum. We would often resort to printing out the code and visually comparing line by line against the magazine.
We mostly had Family Computing magazine. I looked up an issue from 1985 with one of my favorite type-by-hand games, Hit or Miss [0], and no sight of a helpful checksum.
To be honest, the idea of it would have blown my mind back then; the idea that your BASIC code is just a text file that can be processed by other programs is something that would never have occurred to me.
Checksums became popular at some point in the 80s. I remember when COMPUTE! first added them they were a godsend. Especially for the machine language programs that were just pages of data statements.
