Literally some of the most influential journalism of all time has been sourced from anonymous informants that weren't vetted by third parties. We didn't find out who deep throat was until over thirty years later, after he was in a nursing home with dementia.

Remember that anonymous doesn't mean unvetted.

And that leak was over literally millions of lives, so it's not like an intelligence arm of a Nation state doing its job in peace time is so more serious that the standards are higher.