I did post this question at boincstats, but I suspect the problem happened here. That is just a guess but maybe one of the gods here can shed some light.

On a system that has been inactive at BAM! since Dec 22, I noticed a huge drop in credit around Feb 9.

I am guessing this occurred because of a "merge" I did here earlier before switching from BAM! to GRCPOOL. This particular host was originally a core 2 duo and vista and I upgraded (not all at once) both the cpu and the operating system to X5470 and "10". After a while I did a merge and the points got added to the new system that had the same name and MAC address.

Could it be that it took a few months to get around to deducting duplicate credits? I would assume that when the "old" credit got added to the "new" system with the old MAC address that the points would be adjusted at the same time on Boincstats.

Maybe there is some other explanation that is not "merge" related. Howver, this host has been inactive for months so how could the GPUGRID credit drop from 294mil down to 183 million?

There is *more* strangeness in it than what meets the eye for the first sight:
1st: Your host has lost credit, which is strange
2nd: Your host lost credit 6 times, so its source could not be the "merge"
3rd: The rank of your host decreases while its total credit doesn't increase. This could be only if other hosts have lost credits on that day.
4th: Your host (#171317) has 151,883,400 credits today according to GPUGrid.

From your graph, it looks like it took a week before the change (-108mil) or so showed up on boincstats
ie 1-30 on your table to 2-9 on boincstats.

This is what concerns me and I posted at gridcoin about this:

If it takes a week or months for boincstats to remove credits from a merge (I know you say there was none) then

The "extra credits" show up causing a large mining payoff (I am guessing of course), then I remove gridcoin as the "team", wait for the credit differential to be fixed, then register my old system as a new one, join the gridcoin team, and there is no record of the credit differential.

Seems like a security problem.

I am currently mining using the grcpool and there is no way to do a merge while using the pool since the pool is the owner of the gpugrid account. However, once I switch to BAM! and start solo mining, possibly one could game the system using merge or whatever is causing the large credit changes.

From your graph, it looks like it took a week before the change (-108mil) or so showed up on boincstats
ie 1-30 on your table to 2-9 on boincstats.

This is what concerns me and I posted at gridcoin about this:

If it takes a week or months for boincstats to remove credits from a merge (I know you say there was none) then

The "extra credits" show up causing a large mining payoff (I am guessing of course), then I remove gridcoin as the "team", wait for the credit differential to be fixed, then register my old system as a new one, join the gridcoin team, and there is no record of the credit differential.

Seems like a security problem.

I am currently mining using the grcpool and there is no way to do a merge while using the pool since the pool is the owner of the gpugrid account. However, once I switch to BAM! and start solo mining, possibly one could game the system using merge or whatever is causing the large credit changes.

You had the correct account. when I moved to grcpool I removed the gtx1070 board as it was more useful in a newer system with more cores.

http://www.gpugrid.net/show_host_detail.php?hostid=458832

the above is that same host. it was created 3 or so days after I removed the BAM! manager. as you can see it has never processed a single gpugrid wu. It does not show my names as gridcoin owns the account.

I feel better knowing that gridcoin gets info directly from project and not a 3rd party.

GridCoin does not based on BOINCStats, it takes the data directly from the project's servers.