[devilsgrin]

It was always pretty clear that Buffy after dying at the hands of the Master was no longer the official chosen one.
Kendra's death activated Faith as the Chosen One, but since Faith never died - even briefly following her battle with Buffy - no others were called.
Faith's fall into evil made it necessary for the Watchers Council to continue to utilise their most potent weapon - Buffy - who was always the more powerful slayer than both Kendra and Faith...
Buffy's second death meant nothing to the Powers that Be (yes clearly a more angel relevant term, but it fits as those ancient wizards were clearly powers that be inspired) so no other slayers were called.

As to another slayer being called at the end of season seven, they were ALL called at the end of season seven. So there was just one new slayer, there were potentially hundreds, even thousands kicking around.