Wallpaper Folder size limited?

[Devlin2010]

With the 5k iMac its hard not to want a billion photos in my wallpaper folder, but after adding a bunch, and going to system preferences to manually cycle through and see how they look, massive sections of them simply aren't there to be selected, even when they're clearly in the file in finder. Is there a maximum limit of images in a folder for wallpapers? Is there a way to bypass this maximum? Thanks for the help in advance!