However either I am going crazy or this library is either incorrectly descibed or it fails to do the functionality that is described.
Let me take a stab.
You want a library that provides a virtual RAM function using an SD(TF) card .
If that is true, then ALL the operations to the SD card should be hidden (Private) and the exposed (Public) functionality should be (I am not a C++ expert, sorry) RAM operations that look like they operate on SRAM but when SRAM is full make use of SD.