Please verbally smite me if I'm wrong on this, but through my readings I have come to believe that the English definitions are as follows:
-Sempai is someone who was training at the dojo prior to your own joining.
-Dohai is someone who started on the same day.
-Kohai is someone who started after you.
That's pretty much the Japanese definition.
It is considered a permanent title once given, no?
The thing is, it's not a title, it's a relationship. Whether it's a close relationship or distant depends on the people, but it's never "given", it just is.