Looks a cool device to have - I'm tempted - but we know from people's (including mine) attempts to get the 993 OBDII to talk to standand diagnostic equipment that it is quite quirky - ie it does work, but only when the signals are sent and received with the right timing. Durametric have now got the 993 mastered (or at least the "later" 993), but it has taken them many software revisions to get there. I'd be worried that this standard data logger, designed to work with standard OBDII, would not work out-of-the-box on the 993s.
Like Dave, I'm not sure of the date change -but it's quite likely the 1995/1996 model boundary which was the change of quite a few things. (I guess you could call it the start of the "993 GenII" in 997 language!)
If you buy one and it works I like to hear about it.