So, I have been emailing back and forth with Jon, as well as researching, and I think I found a bit more information.
I had an image in a magazine that was of a game at the Polo Grounds from early May of 1903. I couldn't really scan it because of some clutter issues on my workspace, but I snapped a shot with my phone.
There you can clearly see that the leftfield stands are in the same configuration as the Matty photo. So, with that in mind, it's fair to say that they were changed sometime between then and the 1904 photo I posted a page back. I would imagine that the construction happened between seasons, so I would feel comfortable leaving off 1904 as an option all together. Granted, it could have certainly happened during the year - Yankee Stadium in '36 (bleacher configuration) and '37 (right field decks in foul territory) comes to mind, but I figured that it was an alright bet to think otherwise.
Interestingly enough, with the enclosed May of '03 photo, we can also see the actual advertisement on the wall - Pall Mall. It's not the same one in the photo of Matty. Typically, ballpark advertisements were changed in the off-season (though sometimes, it could happen in mid-season or before the World Series, and in some cases, even more than once in a season), so I might guess that the photo isn't from 1903, either. That would put it between 1901 and 1902. And really, if you look at the Polo Grounds Temple Cup lithograph from 1894, the stands seem to have that same configuration.
So, there's no reason not to think that they weren't like that in 1900, Matty's first year with the Giants.
I'll keep looking, but right now, I think the date of the image is somewhere between 1900 and 1902. Now, because it's tough to come across shots of the ballpark from the early turn of the century, I can't really say all of this with 100% certainty. But if nothing else, it's a good place to start.
And if it is from those years, definitely not a bad purchase. It's perhaps one of the earliest images of Matty in the pros.
Graig