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The March 1970 date of this 2.5 x 5 inch brochure (shown as 3-70) can be seen on the bottom of the very last page, which is enlarged below.
The most interesting aspect of this is found on page 4 citing the fact that the cap and barrel has flat end tassies. This fact positively proves that the flat tassies were used in 1970. Another interesting fact is that Parker promoted the idea of using these tassies to personalize the pen with initials. Perhaps this is why they came out with dished tassies and the personalization kit.
It is my belief that some time in 1971 Parker phased out the flat tassies and used the dished version. This belief is supported by the printing date of the personalization kit of February 1971.