This cab is not faded on one side. The color difference is intended. I also have a proto Congo and the cab looks just like this in terms of color. My backbox is actually a No Fear head though, which looks kinda cool IMO.

ok, so I was going by memory and I just double checked mine. It does not look exactly like mine but it is not the same color on both sides either. The difference on mine is that on one side the screen that has the medium green in it has been replaced by blue. It does not look like fade on mine. Mine was never on location either, except I was told it was a game "at the bottom of the stairs", so depends on your interpretation of that.

here's mine for reference.
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Strange, I never thought of it as faded because the blue is so vibrant.

To answer the OPs question though, I personally do value it more and do think it's worth more to the right buyer. While there are many who don't care about the artwork differences, some are really into it. I find the playfield and apron artwork differences pretty cool. I've never really considered selling mine because I like it so much. I would never sell mine for anything close to regular street price, but to each their own. There's plenty of other Cognos out there for people who are not into it.

Mine also had a single slot coin door but I changed it out. And it never left the Chicago area.