I've just been talking to Marcus on the phone and he asked me to update this topic for him: Marcus has found a Loetz Enigma jug which now he can compare with the Smrckova version as above and has noted some important differences....
The handle on the Loetz jug is applied, it is not an integral part like the Smrckova version. On the Loetz version two holes are made in the body and the handle which is made from a hand-rolled piece of glass is applied into the holes.
The base of the Loetz version has a polished pontil mark also, whereas the Smrckova does not.
The finish is noticeably different also, the Loetz version, although craquele, is smooth to the touch, whereas the Smrckova one is quite sharp and rough to the touch.
The quality of the Loetz version is much superior to the Smrckova version. I think that covers the basics, though Marcus may add more when he's next on the board.