Nat China apparently did get a few (along with the Pz1, Sd221 etc), so these would have arrived sometime between 1927-38, when the German mission to China ended.
My best guess - use the same ISD as the German-supplied Pz1, ie 6/36 to 12/37 (when the armoured battalions were wiped at the battle of Nanking).
http://en.wikipedia.org/wiki/Develop...281927-1945%29
Assume that they had all the new German kit concentrated in these formations?.
Wiki gives an ISD of 1934 for the SfH18 in Germany, the OOB currently has 1936. Probably more believable than the nat Chinese having them first, unless export orders were expedited over home?. I would say, move the ISD in Germany back to 34, not as if it would impact anything "historical".
Andy