B1: 7/18/15, K1: someone1@emailhost.com
B2: 7/18/15, K2: someone2@emailhost.com
B3: 7/18/15, K3: someone3@emailhost.com
B4: 7/18/15, K4: someone4@emailhost.com
B5: 7/18/15, K5: someone4@emailhost.com

B7: 7/19/15, K7: someone5@emailhost.com
B8: 7/19/15, K8: someone5@emailhost.com
B9: 7/19/15, K9: someone6@emailhost.com
B10: 7/19/15, K10: someone6@emailhost.com
B11: 7/19/15, K11: someone7@emailhost.com

P6: 7/18/15
Q6: 4 (using this formula: =SUMPRODUCT((K1:K5<>"")/COUNTIF(K1:K5,K1:K5&""))

P12: 7/19/15
Q12: 3 (using this formula: =SUMPRODUCT((K7:K11<>"")/COUNTIF(K7:K11,K7:K11&""))