The lists of bilateral visits have been compiled from one main source: the collection of files transferred by the seven federal departments to the Swiss Federal Archives (SFA). Some 4200 files have been evaluated.
Other sources have been consulted, in particular the (annual) Business Reports of the Federal Council, the Yearbook of Swiss Politics (published since 1965) and various lists of visits produced since the 1960s by Protocol of the Federal Department of Foreign Affairs (FDFA).
Problems of incomplete information became apparent as follows:
- In the inventories of some departments which did not compile a list of visits or at least not systematically
- In the transfer of the files to the SFA which was not systematic until 1990
- In the contents of the files, of which some were incomplete, it was not possible to confirm whether the visit actually took place and whether at least one member of the Federal Council participated