They had no idea their notes would ever be public. There were no public disclosure laws at the time. The notes were verified twice by other agents before being submitted to the record. It's not like "oh, allegedly this happened". It's not a narrative. This fact comes from a transcript of an audio recording, which is actually going to be released in a few years.
They recorded him because they didn't like him. It doesn't change the contents of the recording, and it is perfectly in line with everything else we know about his debaucherous sex life. The feds blackmailed him, right? With recordings, right? And in order for blackmail to be successful, the material needs to be real, right?
The man who published the findings is a pulitzer-prize winning biographer of MLK with zero motive to lie.
Hard pill to swallow, but very very real.
They only need enough to justify keeping her in custody. More can emerge later