I am not convinced by the provenance history of the VMS

[oshfdk]

In the 20th century, maybe. But these people allegedly owned the VMS from the 17th century onward.

300 years earlier, why would it be faded at all?

And even if it was a little faded, these were manuscript experts. It would have been trivial for them to remark such a signature.

1) It was likely erased, not faded, so it could have been erased before Marci and others could see it.
2) Reportedly, Voynich didn't see it either, until he saw the photograph of the first folio that he had taken. It's quite possible that the sensitive B/W film could capture more than the eye could see, for example some extra short wavelengths. Then Voynich tried to enhance the signature chemically. It's not impossible that prior to this enhancement the signature was completely invisible to the naked eye.

Edit: I think this has been discussed many times, it's quite possible that mentioning naked nymphs would be a faux pas in correspondence (Kircher was a Jesuit priest, if I'm not mistaken) and the balneological section is relatively short and its main feature, again, are bathing ladies, otherwise the manuscript is mainly plant images and some cosmological diagrams, which seems a correct neutral description of it.