Key legal question
Whether the Lucerne tax claim was forfeited because it was asserted too late in a reassessment procedure.
Extracted holding
Yes. In a reassessment context, the competent canton must act as soon as it knows or can know the decisive facts; Lucerne waited unreasonably long.
Extracted reasoning
Basel-Stadt had assessed and collected taxes in good faith. Lucerne only initiated reassessment in late 2011 for nine periods, although it should have known earlier of the alleged residence shift; this breached the stricter diligence required for reassessments.