Stranger in a Strange Land was popular enough and written late enough in Heinlein’s career that I’d be somewhat surprised if movie options truly earned him more than book sales (I mean, “stranger in a strange land” and “grok” both entered common parlance)–then again, it’s possible Heinlein got a shit contract for that book, or there were some heavy-hitters optioning the movie for tons of money even if it never got made. He was savvy enough too that he might have jacked up the cost of optioning the book a lot if it was getting a lot of Hollywood nibbles. So maybe it’s not urban legend.
I bet some sci-fi author out there knows if it’s true or not.