The one piece front, or 3/4 vamp boots we know are common to the pre-CW, CW and early western frontier era are clearly correct with many images of such, that is until the 1880s when you started to see boots with the 1/4 front bottom quarter sewn in becoming increasingly seen, and by the turn of the century common. Others knowledgeable on the evolution of boots will way in regarding the beginning use of the later - perhaps very early.
However, I am well aware of images of CW era boots that do have the 1/4 front. So, they could be correct although the one piece front would seem to be far, far more common. All boots specified by the military up until the later part of our period were one piece front unless private purchase - per literature I have read describing specified construction. Be glad to provide sources if you need them. Not a boot guy but I have heard it suggested, although not seen it discussed in period literature, that such construction was more expensive and generally required additional payment for such a product. Start with Echos of Glory for supportive information on boot images from CW.
I have found no images suggestive of "spur shelves" in the 19th century, or even much of the 20th century. I have never read any period reference using the term spur shelf. Although you see them on boots sold by modern sutlers today, boots purporting to be "old west style" and even those designated as "cavalry boots" I submit that failing any evidence to the contrary they are absolutely incorrect - and by the way a solution to a non-existent problem. To the best of my knowledge they started to appear on modern "buckaroo boots" which have a higher larger heel than most other cowboy boots today. Although nifty looking as I even have a pair worn frequently out and about, stay away from spur shelves unless someone else can provide evidence I have yet to see.
Delmonico: you posted while I was writing this - Spur ledge on an 1860 boot with "cuban heels". Man, what is your source for that? Do you have any images? This is new information for me - sources, sources sources!!!! I would be truely interested. Was the term spur ledge used?