referencing different version of unityengine.dll

I am writing a library which is used in unity users, of course, in dll file format.
My library will reference unityengine.dll, too.
However, will it be safe if the version of the referenced unityengine.dll in dll builder computer is different from the version of the unityengine.dll in other user computer? (for example, my library dll is built with unityengine.dll v3.5 and the library user uses unityengine v3.4?)

they are referenced, as such the one within the local unity will be used. if you used classes and functions not found on 3.4 it will lead to an error in the editor console mentioning the missing class and thats it, so you would have to inform the user that it requires 3.5 or distribute it through the unity asset store then with a package built by 3.5 as thats only downloadable then from unity 3.5+