Another way to determine if you bought an art work is once placed on the back of the art if genuine it has a label on it the fake version doesnt only applies to the pictures.

I also heard that fake art is haunted and can move depending on what it was a forgery of

Yes you can still get him I believe, to check whether he is there or not you just look at the map and check if redd's leaf symbol is there (it looks different then nook's leaf symbol) on the secret island that I believe is only accessible with a ladder. I could be wrong though.

You may have to talk to him twice

Uhh i missed redd ;-; can I still get him?

 Click to Enlarge

You have to find Redd first

I updated my game but when I go to Blathers he doesn't mention anything about artwork. What am I doing wrong?

yeah its a thing here's the link
https://i2.wp.com/www.masterpiece-of-japanese-culture.com/wp-content/uploads/2016/08/470px-Ito_Jakuchu_AjisaiSoukei-zu.jpg?resize=470%2C768

The pic under the 'whether it's fake or not' thing is fake. The original has blue flowers instead of those magenta-ish ones, search this up: Rooster and Hen with Hydrangeas