In the report, except conversion report, the offer’s all statistics will be recorded to advertiser B (the new advertiser), include the previous statistics and the future statistics. In the conversion report, the conversions will be recorded in the advertiser which the conversions passed from, so the previous conversions will be recorded to advertiser A, the future conversion will be recorded to advertiser B.
But in “manage advertiser->advertiser list” page, the previous statistics will be recorded to advertiser A, the future statistics will be recorded to advertiser B. 
So please check all statistics in the report.