I acquired these two older jack knives this week. One with the black handle is a Wostenholm I*XL. The other is a Boker. The stamp is H Boker & Co Improved Cutlery. Goins list this as 1860-1914. I have included the marks on this one in case someone can help me to narrow down the age range. The blades on both knives are nice and tight with good snap and half stops. The small balde on the Boker has obviously seen quite alot of the stone over the years. 
s-k
Your closeup of your tang stamps are great, what camera are you using to get those...
s-k