Having compared this with another early loopstay Yeti Ti i would put my money on that being genuine. The early Yeti Ti frames were made in-house, the later ARC ones with the machined dropout were out-sourced, which would explain the quality difference as Yeti were not a renowned Ti house.
There are many features on that which are exactly the same as the early Yeti Ti frames, but there are a few features that say it was an employee frame rather than a production one. Obviously the finish is, well, unfinished as it's not been brushed. The second issue are the cable stops on the TT which were ARC type riveted ones on the early production ones but are welded on this one. The radius of the rear loop is perfectly matched to the early production ones and the drop outs look the same although there is a subtle difference on the non drive side. Finally the welding is 'interesting' on that one (although, I was told by someone in the know, that the Yeti welder responsible for the early Ti frames could be a little erratic in his welding).
I would say that it is an early 1999 loopstay yeti titanium, but maybe it was an employee learning the ti welding skills from the in-house welder, or maybe it was a rejected frame due to it's 'issues' that couldn't be sold but was saved from scrap.