Very, very few are actual OEM. Most of them absolutely guarantee they are and show pictures of real ones. They are not. Sometimes their fine print says they have so many "real" CD's they can't take pictures of all of them and yours may just be a different model. Some have stories about how they search flea markets and other places for them. Right now I see your 4115 for $29.95, and another 4115 for $16.99. I have checked some of the Ebay CD's and found most to be crude attempts at labeling pirate copies. About the only way to get a used real OEM one is find somebody who kept their CD after selling their tractor. The absolute, but very rare, best way is to find a John Deere dealer who is selling spare disks on Ebay. They usually include several models. Having said all that, the pirate ones will typically have the JD service information on them and you may be happy with that.
i was quoted for repair manual for 4720 tractor 700$ for teck manual 1100 pages didn't order yet but thru ebay was disappointing but that was for jcb backhoe