I have found a strange thing. I have sum all my credits in "My detailed stats" and get the current credit 'x'. If i follow the "link to user host stats" and sum all credits for my hosts i get the value 'y'. I don't know where comes the difference between. But if i sum to the host credits 'y' my one and only retired project (RS) i get a new value 10k credits back to the value of current credit 'x'.
I know both values could be vary in dependence the time of update.
Sometimes projects give credits either to user or to hosts due to some reason.
For instance, on June 6th FreeHal gave 1000 credits to each host crunching this project. These credits doesn't appear in user credits.
Another example is Cosmology where users got 5000 credits (somewhere in April I think). No credits for hosts this time.
These are two reasons for the difference between user credits and sum of host credits. Propably there are other reasons as well.