Calcbench groups tracks companies by accounting history, not legal entity. When two companies merge one of them becomes the acquirer for accounting history purposes. The next 10-K/Q usually states which company has been designated the acquirer.
For example, in 2015 H.J. Heinz (HNZ) merged with Kraft Foods Group (KRFT) to form the Kraft Heinz Co (KHC). The intricacies of the merger are explained in Item 1 of KHC's 2015 10-K.
The history of the relevant entities is as follows -
Mondelez spun off Kraft Foods Group (KRFT) on October 1, 2012.
H.J. Heinz (HNZ) was purchased by Berkshire Hathaway and 3G in June 7, 2013.
On July 2, 2015 Heinz merged with/purchased Kraft and began trading as KHC. Because Heinz was the acquirer for accounting purposes the history we have for KHC is the history for Heinz, not Kraft.
Calcbench reflects this as follows -
We have history for KRFT from 2010 (two years of history from the first 10-K they filed after spinning out of Mondelez through 2014, when they were purchased by HNZ/Berkshire/3G.
We have history for KHC from two years prior to the beginning of the XBRL mandate, 2008 through the most recent year 2017. That includes the period when Heinz was owned by Berkshire/3G, they continued to file financials.