Looking at RCN stats for BOINCstats team I see discrepancies between team credits and the sum of the members credits. The difference should not due to some timing because seems much more than credits obtained in the last day, so where I'm failing in valuating the team stats?
Same for Spinhenge in BOINCStats team stats.

Credits for team stats are only added at the time of granting, and when the user is member of the team at that time. Sum of members should nearly always be more then team. Only exception is CPDN & Co, here the credits will move from team to team.

Another exception - if someone leaves a team (not CPDN/SAP/BBC) the points stay with the team (as you said), but this'll mean the sum of the members is now less than the team total.

For Spinhenge the team credit is 1400 sum of members is over 4000.
Members are about the same as yesterday.
I refer to Spinhenge and RCN just because there is a short members list and it easier to check than... Rosetta.

Take a look at this: click

It shows the credits each team member had when they joined the team on Spinhenge. The numbers add up to 3284.

For RCN it's a similar story: click

It's clear.

thanks Marky-UK