OT: The calling of a new slayer

[jetthd@xxxxxxxxx]

I'm curious about how a new slayer is called. I'm working on a story 
and would like some input on this topic. My dilemma is that in the 
movie (if memory serves) it was mentioned that Buffy was called later 
than normal (was older than most when called). Yet in the series we 
have Kendra and every indication is that she knew before she was 
called and had been training since she was young. If there is 
foreknowledge of who the next slayer will be why wasn't Buffy told? 
And what would happen if a slayer-to-be is killed through some 
accident or even a deliberate act. For instance, what if Kendra had 
been killed in an automobile accident a few days before Buffy 
died/drowned. Is there an alternate slayer list? Maybe that was the 
situation with Buffy - the primary slayer-to-be was incapacitated so 
Buffy was pressed into action. Anybody else have any input on this 
topic - Please?