While the documentary is quite detailed and well organized it has pro-Russian and anti-Polish bias.
It perpetuates the false statements used by Soviet (and nowadays Putin's propaganda, see S. Lavrov books) about Polish Minister of Foreign Affairs - Józef Beck.
The claim about his alcoholism is a product of Soviet and Putin black PR, not supported by any documents.
The same can be said about incorporation of part of Czechoslovakia by Poland after Munich pact. Nowhere it was said about Polish inhabitants in this part of Czechoslovakia, or about the fact that this part of Poland was illegally taken by Czechoslovakia in 1919 during Polish-Soviet war.
I think that these omissions of crucial facts and false statements renders the documentary unreliable.