Reading a fascinating online book about the history of computing, I came across this passage on http://ds-wordpress.haverford.edu/bitbybit/bit-by-bit-contents/chapter-seven/7-5-assembly-language-programming/
The original FORTRAN compiler ran only on the 704, but programmers went on to develop FORTRAN compilers for other IBM computers, and competing manufacturers, licensed by IBM, adapted FORTRAN to their own machines.
Wait a minute. Competing manufacturers, licensed by IBM? In those days, you couldn't patent software. You couldn't even copyright it. Even nowadays, thanks to the recent Supreme Court decision in Oracle versus Google, it is legal to write your own implementation of someone else's programming language.
So why would other manufacturers need a license? Why would there be any legal problem with them just going ahead and unilaterally writing their own Fortran compilers?