Because statistics on delivered Messages include some Contacts that are ALSO in the statistics of Bounces. Why?
This happens because some servers that accept an Message return 2 codes, one code saying "ok" AND another code saying "error".
This seems strange but it's the reality.
In Ofsys, for these cases, we calculate like this:
+1 in DELIVERED Messages
AND +1 in BOUNCES
So the equation is :
( [Bounce_Hard] + [Bounce_Soft] + [Stats_DeliveredCount] ) – [Messages in DELIVERED AND in BOUNCES] = [Stats_MessageCount]