Same sort of thing occcurred when I did one of the Aarons rephoto, the one with the commemorative plaque. I first spot a corner that looked to be the right one, but with a different plaque and took few shots. Only to figure out later on that the wall pattern was indeed different. I had to go back and look for a similar corner, which was not that obvious.
Also doing all those rephoto I realized how difficult it is to match the exact same perspective of an existing shot (actually it is impossible with a different lens)