Definition of "thrillproof"

It was a team which played so thrilling a game that during the last five minutes all but one of the supposedly thrillproof sportswriters forgot to write.

1990, Brad Pearson, A Roar from the Valley, page 78

Kids nowadays were a right thrillproof bunch. The Armoury Section had, unexpectedly, proved to be a real moodclunker.

2015, Jeff Torrington, Swing Hammer Swing!, page 255