To answer you about that japanese Sawsbuck of yours, let me just ease your conscience:
"In Black, White, Black 2, and White 2, the foreign Pokédex entries are also the same as in Platinum, just like native entries. However, only non-Unova Pokémon receive foreign Pokédex entries. For Black and White this is likely because foreign entries and names of Unova Pokémon had not been finalized yet at the time of the Japanese release of Black and White. However it is unknown why they were not included for Black 2 and White 2 as foreign Pokédex entries for Unova Pokémon would have been available from international releases of Black and White."
So Bulbapedia basically states that Unova Pokémon cannot have foreign entries, even in Black and White 2, thus your Sawsbuck is still viable for the Masuda Method and you're just being paranoid a little bit.
If you really want to make sure you're having a foreign parent, just catch a prior-to 5th generation Pokémon and trade it to your english Black 2 and see if you get the Japanese Pokédex entry.
I hope I helped!