Every now and again, Antiques Roadshow (don't judge me, I'm cool and so are my hobbies) will have an updated episode kind of thing, where they go back to an old episode from a decade or so ago and show what the same pieces would be appraised at todays dollars. Sometimes they go up, sometimes they go down, sometimes they only go up enough to account for inflation. A lot of these pieces are famous pieces by famous creators, studios, etc. and even then their prices are volatile and based upon purchasing fads (which probably creates a price feedback cycle). So with that in mind, something crazy like a Da Vinci would be a safe bet. But I'd only make that statement about a verified Da Vinci. The fact that this painting is attributed to Da Vinci and then followed up with a question mark and a caveat, does make it seem like maybe it was a little over payed for. What do I know though? To me, a million dollars is an unfathomable amount. The gap between 1 million and 450 million is unfathomable and 450 million is pretty much out of the realm of my imagination. Plus, I got chastised recently for having "pedestrian" and "uncultured" taste in art so this whole thing is really out of my realm.
There's a lot of question marks and caveats about art from 500 years ago. There were a lot of studios run by artists whose art was painted by someone else, and often that someone else became someone famous and opened his own studio, so provenance is often shaky. I mean, Warhol has only been dead 30 years and this shit still happens.