Martin explained to Tyson that he likes to do as much research as he can, and then decides how his version will remain faithful or lightly distorted opposed to other interpretations.
Unicorn talk aside, a large part of this Startalk with Neil DeGrasse Tyson conversation was rooted in George R.R. Martin talking about the process that goes into his writing.
After listening to the amount of research he puts into each subject, it’s understandable why it’s taking him so long to finish the books.