the dates we chose are from my collection of original c7 & c9 dearborn flat type solinods since these were made in batches. I have had many of these over last 35 years besides 69 dearborn mustangs & cougars these were used on some torinos, 69 1/2 mavericks ,some pick-ups etc. all depending on the vendor used at that time just like trico vs anco wipers, TS vs GE headlights.