According to klingenfuss.org, the northern end of the Grande Traversata della Alpi (GTA) is near Valsesia (Monte Rosa) or at the Val Formazza. Wikipedia has it start west of Domodossola (consistent with Klingenfuss), according to gta-trek.eu the northernmost point is Alpe Devero, north of Domodossola and west of Val Formazza. Cicerone Guide describes a conclusion near Monte Rosa (consistent with Klingenfuss) and Rother Wanderführer appears to place the northernmost end at the Passo San Giacomo between Val Formazza and Val Bedretto, a bit further north than the rest.
However, I took this photo near the Rifugio Bonasson, well east of Val Formazza, high above the Agrasino, further east than any of the aforementioned sources mention the end of the GTA. The photo indicates the GTA in the direction of Forcola di Larecchio, Bocchetta di Muino, or Alpe Lago. Apparently, neither Valsesia, nor Val Formazza, nor Passo San Giacomo is actually the most northern/eastern end of the route (meaning furthest along from the Mediterranean).
Where is the furthest north/east on the GTA, really?