Window Sticker question

[MYSTERYCHEVELLE]

As many of you may or may not know,... I am heavily involved in the 66 and 67 Chevelle SS cars and the facts and details of them. Part of my research has involved, like many here, looking at many many original cars and original forms of documentation. One of those pieces of documentation includes Window Stickers. Sorry, for the intro., but I always think it important to know why a question is being asked.

Now, I know repro. window stickers., have seen the good, bad and Ugly ones! So this isn't about how to spot a Fake, but I was curious if some of you could give your thoughts on the bottom section of the window stickers...the part which commonly says, " based on excise tax ....whatever month and year..."

Is that excise tax information line always on the sticker? I mean, almost all 66 and 67 Chevelle stickers I have or have seen, do have this...but was it a Given, was it required to be on the sticker? Did it start being placed on stickers any particular year or was it limited to any particular region of the country? looking for any and all information on this little but important detail of original window stickers.

Thank you

Mike Crown