There is a lot of confusion on this one. I think part of that confusion is also driving the price.
The white cover has been come to be accepted as the "Sketch" cover. There were 6500 printed and came with a COA stating: "Amazing Spider-Man #1" Marvel Authentix Limited Edition Comic as one of a specially limited series of sixty five hundred copies. This book was released 12/16/98.
In January 1999, Marvel released a version with John Romita sketching the box with a Spider-Man head shot. There were 300 printed and came with a COA stating: "Amazing Spider-Man #1" Marvel Authentix Limited Edition Comic "Sketch Cover" as one of a specially limited series of three hundred copies drawn by classic Spider-Man artist John Romita, Sr."
After this, there were also signed versions by Stan Lee, another Romita sketch version, and one signed by Stan, John, and John, Jr.
All of these though are the same white cover as the 6500 printed run. So, there is only one cover of the Authentix book. It has been signed and sketched on.
Not sure why CGC lists these seperately. If you look under the 'Marvel Authentix: Amazing Spider-Man #1 Marvel Authenix Sketch Cover' listing in the census, you will see 76 qualified issues, which are most likely the sketched upon and signed (non-witnessed) books. I have asked what the 'Marvel Authentix: Amazing Spider-man #1' books were, but never received an answer.
Lastly, I feel because of this sketch label, prices seem unreasonable high on this book with a 6500 print run. Maybe because the original Romita sketch issues were going for good money, that confusion set in, and now everyone thinks this is a $100 book?
Anyway, hope this helps.