I guess it's appropriate that 500kc/s should be used for Navtex. Unfortunately, it was the failure by a few R/Os to copy Safety (TTT) nav warnings after the old silence periods that led to the famous 1970s disasters when ships ran full speed into wrecks in the English Channel that led to the introduction of Navtex.
Now Navtex is an integral part of GMDSS. Of course it can also be ignored by the navigation watch officers. But I have noticed that most ships I board in the course of my job have a system for checking and filing the print-outs. They can never complain they didn't get the warnings.