I am unable to use the DUAL SPLIT button effectively after another effect has already been placed on it... wether or not its on the bottom layer or not....

In other words, the picture editor used a resizing method or 3d zoom to be more precise... and that's on one level... IF I apply a grade I can no longer use that DUAL SPLIT button to look at a before and after shot...

Any ideas?

Dual split works strangely if you have an effect on a clip.  Your best bet then is to jump out of CC mode, load the original source clip in the source monitor, and toggle between the source and record.