There are 13 named potentials in Buffy's group in S7, the 9 who make it to the final battle plus Eve, Chloe and the two who Caleb kills.
There's a recurring actress creditted as just 'Slayerette', who I assume is a potential, and then 7 actress who appear in various different episodes creditted as 'Potential' or 'Fighting Potential', bringing the total count up to 21.
However looking at some of the group shots, I suspect there were some uncreditted extras.
Does anyone know of any better sources that just counting the credits for how many there were?