5987 IS NOT AN SCP! IT'S SIREN HEAD!

Siren head was proposed to the SCP Foundation site as the non-canon SCP-6789, but it got removed by the Foundation, and they stated that Siren Head is not an SCP. Any source implying Siren Head to be a SCP is false, since Henderson has stated that he wishes to keep Siren Head as his own separate work.

Yes

In a nutshell, Henderson pulled trademark.

YES

Imagine giving Siren Head an SCP number while telling people it's not an SCP so you confuse more people.

"SCP-5987 is NOT an SCP! It's Siren Head!"