[popcornmix]

I still have my, how do verify rendered/output in full 3D?

HDMI capture card, HDMI analyser or HDMI device that gives detailed info about the HDMI mode.
Without that, start playback on 3D TV. Whilst playing, unplug and connect to 2D TV. Then connect back to 3D TV.

If 2D TV displays an image (e.g. half-SBS or half-TAB) then you know it is not frame-packing.
If it doesn't display an image, and you still have an image when connecting back to 3D TV then I'd be pretty convinced it was outputting frame-packing.

This assumes that the 2D TV does support the 2D HDMI mode (e.g. 1080p24).