There were three mergers of municipality in 2012 (see http://www.bfs.admin.ch/bfs/portal/de/index/infothek/nomenklaturen/blank/bla...), all of them in Ticino. I've tried to fix them correctly as there led to annoying white holes in my road name statistics, however there may be errors, particularly with higher level administrative entities.
The old relations are tagged with boundary=old_administrative, just as boundary ways that are no longer needed.
Simon