Doesn't a horcrux have to be made at the moment of a killing? Or do you think Voldemort had the horcrux object with him and somehow just hid it in the office? It couldn't have been created there, I don't think. I am still wondering about the Sorting Hat, which belonged to Gryffindor, but I think it is unlikely. I also have been wondering, does anyone know how Harry's parents and Neville's parents "thrice defied" Voldemort, per the prophecy? I think Dumbledore says only they were in the Order and had escaped three times.
I just don't think Harry's scar is the horcrux. I think the entire person or creature would have to be the horcrux, not just some physical feature of that person. As for the article, I don't think Hermione's failure to research Regulus Black is significant. As far as I can tell, Regulus was not a well known wizard; why would he even show up in the books? I can't recall if Hermione is even present when Sirius mentions his brother to Harry.
I think it was in OOTP when they were taking a break from doxie killing when he mentioned Regulus. Hermione was there, but I don't think she was involved in their conversation.
I don't think so, but this is all speculation on my part. In Slughorn's memory, Riddle was wearing the ring, but (I assume) he did not, at that time, know how to turn an object into a horcrux. At some point, IIRC, DD mentioned (or at least supposed) that Tom/VM made horcruxes from significant deaths--at least, that's what I remember. I know DD made it clear that VM chose the objects which would become horcruxes based on their significance. The death of Tom's father would certainly have been significant; I believe that it was that murder, and the resulting "splitting" of Tom's soul, which enabled Tom to eventually make the ring into a horcrux. Again, all speculation. All we really know about the creation of a horcrux is that it requires an act of murder--that much has been specified by Slughorn.
I think you have to do a murder in order to split the soul for the Horcrux. They never mention the timing needed to store it somewhere. I think you have to just know the spell or whatever to put it in something. Not sure though.
"I just don't think Harry's scar is the horcrux. I think the entire person or creature would have to be the horcrux, not just some physical feature of that person."
That said, what about Professor Quirrell being used
by the parasitic Voldemort? Both were able to function
independently despite V's having ensconced himself
inside Quirrel. When Quirrel died, V left to find
another host.