Why was there no plebiscite in the part of Upper Silesia that was given to Czechoslovakia?

[Futurist]

Why was there no plebiscite in the (small) part of Upper Silesia that was given to Czechoslovakia? It seems rather unfair to hold a plebiscite in the rest of Upper Silesia but not in this specific (small) part of Upper Silesia, no?

[Cekekb]

It was granted outright to Czechoslovakia by article 83 of Treaty of Verailles.
Czechoslovak delegation was able to present fairly strong historical a and ethnical arguments - area in question was until 1742 mostly part of Opava princedom and Moravia and it had majority of Czech-dialect speaking population.

[Futurist]

The ethnographic argument is interesting but ultimately it wasn't enough to secure the rest of Upper Silesia to Poland without a plebiscite--or, for that matter, to secure Teschen to Poland. The historical argument is more interesting. 1742 is way after the 14th century, which is when Upper Silesia stopped being part of Poland, if I recall correctly. I suppose that a three-way plebiscite might have also been more logistically difficult to conduct than a two-way plebiscite would have been.