DiscoveredUsbPrinter doesn't exist in latest version???

Have installed the last version of OS link sdk, then have réferenced to it on Visual Studio by the NuGet Packaging manager, and lastly have added "using Zebra.Sdk.Printer;" and "using Zebra.Sdk.Printer.Discovery;".   Nevertheless, Visual Studio, only aknowledges the existence of DiscoveredPrinter (which is a virtual), but not of its instances like DiscoveredUsbPrinter.   It's like they don't exist in the library.  What might be wrong?