Just in case i missed it somewhere in my searches for this answer, i am curious about the “Use Last XY Zero” button when setting up a carve. Last night i carved out a tool path that took 4 hours and instead of changing bits and finishing the last cut, i went to bed (rather late to boot). Today I am ready to finish the piece and in the process of changing bits the x and y both moved on me. I have homed my machine and set the Z zero with the probe. So now the button mentioned above, will it use the settings from last night even though i logged off and its been 15 hours or so? Or does it only look for recent setting since the current login? I ask because if this screws up, i will have to sit through 4+ hours of the other carve again… no thanks! 
It moved while you were changing bits, then the last known position isn’t where the machine thinks.
Yes, as you know I just recently got my homing switches installed. So my thought process is still a little out dated lol.
So maybe my thinking is off here, but I’m putting it out there anyways.
I agree that the X, Y and Z of the spindle have not changed and are in the controller and if he homes it would then allow him to utilize the “Use Last home” button, but wouldn’t that ONLY work if the bit he changed to was put into the collet and adjusted to stick out of the collet the exact amount the last bit did?? Otherwise his X and Y would be perfect but the z would think it’s right but the new bit he changed to would be either higher or lower than the other.
Just thinking out loud.
Gotcha, thanks for the clarification.
Thanks a ton for the responses guys! I waited for a response for about 30 mins yesterday and just tried it. and it worked fine. although i think the right side of the Y was off still though, the ellipse i was cutting was centered, but a little wonky on the final product. still looks good enough to go with though.