Hi Daniel
I think there were around six or seven generations
The earlier the better and this is down to how well they were made (the devil is in the detail)
You will find examples on the web for the mei (signature) and I suppose this is late around 1850
Early Edo is post 1600 so much later than suggested
The mei has been cut into for fitting on another sword so some liked it
Nothing wrong with an honest tsuba and a nice gift
Although there are many Kinai tsuba they are not a 'collectors' item unless of the highest quality but someone called James Lawson has bought the best ones!
As these are not too expensive you could look and maybe buy these from the internet and if you do pop an image on this site stating the price if known to ensure it is not a copy
I have four Kinai for sale on the items for sale on this site, the post is called 'Massive Tsuba Sale'
I'm not interested whether you buy or not but worth looking as Kinai examples
Grev UK