The following problem exists in many databases, but I only have one example at hand at the present time. So I'll post the example I have.
In the U.S. Phone and Address Directories, 1993-2002 database, it's possible in Old Search to search by phone number. It's not possible in New Search.
There are numerous cases where a data element from an Old Search template does not exist in the equivalent New Search template. I think that all such omissions should be corrected in the New Search templates, certainly before Old Search is turned off.
Sometimes I can get around such problems by searching for a data element in New Search as a keyword rather than as a data element. Doing so is never as satisfactory as searching directly for a data element, but it's better than nothing. In the case of the phone number in the U.S. Phone and Address Directories, 1993-2002 database, searching for the phone number by keyword does not seem to work.
I labeled this as an "Indexing and/or Template Problem" because I don't know if the problem is just a template problem, or if the indexes for New Search do not even include the phone number as an indexed field in the U.S. Phone and Address Directories, 1993-2002 database.