I'm starting Ed Friedland's Building Walking Bass Lines book (no tabs - sweet!

) and have a question about key signature and how it impacts the piece.
Mind you I have rudimentary understanding of reading music - almost through book 1 of the Complete Bass Method (another Ed book!).
The first piece in the book for part one is written in Bb. So on the staff you've got the standard F-Clef symbol, a b (flat) symbol on the B line of the staff.
That means that all "B's" in the piece are played flat regardless of octave because the Bb major scale contains no natural B's right?
Also while this piece (12 bar blues) contain's no E's, if there were E's to be used here they would be flat as well since Bb scale has 2 flats (B & E)
Am I right here?
EDIT: NM - I read it wrong, there is only a single flat on the staff, this piece was written in F not Bb