I find these scientific examinations of artworks very interesting, both from the historical/technical side and the esthetic side. One of my favorite YT available TV series is "Fake or Fortune" from the UK, where they do such examinations including provenance, etc. Both entertaining and informative, and I wish they had new series available in the US. "Starving artists" reuse canvases, but so the the thriving artists, as they work out their ideas or reject some. Anything new that is authentically Van Gogh is informative. The guy isn't painting anything new lately! LOL All my stuff from the past decade or so is documented via one blog form or another, so when I'm gone and famous, you'll be able to research it easily without involving the Courtald Institute.... ;=)
Sadly i forgot the artist name, but something simliar happed about an abstract american artist.
While looking at the canvas more close, someone noticed that some green paint at the back of the canvas, even though there was no green in the painting .
Then they noticed that the artist glued a pice of paper on the previous painted canvas and then had painted the painting. Under that painting was a long lost work of the artist.