When merging contacts, the default behaviour is to keep the latest value for each property. However, this does make zero sense for certains properties like “Original source drill-down 1/2”!
Anything related to original source should default to oldest value, as is the case for “Create date” already.
In an ideal world, one should be able to specify the merging-behaviour for each property; other options needed than “keep latest” and “keep oldest” would be sum for numeric values.