I would appreciate help in dating a Vintage Oshkosh B'Gosh Denim Overall Dress. I have provided pictures of the dress, the buttons, & the labels. The rectangular label on the front says, "OSKOSH B'GOSH Unionmade Sanforized'. The label on the back is a triangle with green & red lettering that says , "OSHKOSH B'GOSH VESTBAK UNION MADE.' The button looks like a green shamrock. What year/decade do you think this dress comes from?