5 different sets using the same fronts. 
Sen-Sen Gum issued sets of 50 birds in both the US and Canada. 
The US set is listed as E225
The Canada version is V120. 
 
US set backs - Philadelphia, PA
Canada set backs -  Toronto, ON 
 
The US set was issued 3 times:
    1. a plain front and the back advertising
        a bird album for the cards
    2. a plain front and the back advertising
        a bird book for the cards
    3. Chiclets printed on the front & back and
        the back advertising a bird book for the cards. 
 
The Canada set was issued 2 times:
    1. a plain front and the back advertising
         a bird book for the cards,
    2.  Chiclets printed on the front & back and the
         back advertising a bird book for the cards. 
 
The plain fronts are identical for the US and Canada sets and
the Chiclets fronts are identical for the US and Canada sets.

A master set would total 350 cards