In my experience, typically...conversion tracking is usually accurate.
There may be a case of post-upgrade-effect, though even in
those events...it should be corrected asap within a day/s or sooner.
(ensure that conversion tracking is selected in bulk edit at the account
level. Sometimes the script may be dated ie: if you are using the script
from last August...just copy the newer script from campaign or
adgroup settings and paste onto your appropriate web page.
My clients are not reporting post upgrade issues with conversion tracking,
perhaps the adCenter people can move your case to be researched.
Hope this helps.