The turk M1866s were probably scrapped for the brass value of the frames.
A German purchase of 8000 M1895s would be about 9% of the total M1895 production less the Russian contract and would be well known.
The quote says Belgian made. 8000 does sound like a lot for a trial. Moderate numbers of rifles can certainly disappear, all that would need to happen is the rifles were unsatisfactory, sold to ALFA and then sold to Abyssinia or China or one of the other dumping grounds. Supposedly they were issued to a Saxon regiment, so there is a good chance that any record burned up in 1945 in Dresden.