The first Dura-Ace stems and posts were part of the Dura-Ace EX group (7200 series). While this group came out in 1978, the stem and posts weren't added until 1980. They were then adopted for use with the AX group (7300 series) in 1981. Both EX and AX stems were produced concurrently until 1985, when they were adopted for New Dura Ace (7400 series). The first stem appears to be New Dura-Ace EX, the second appears to Dura-Ace EX, while the last could anything, including 600AX (6300 series), though are are generally identifiable via a blue plastic cover for the hidden expander bolt. Regardless, all the parts should have double letter date codes which you can decypher to determine the exact year, using the information on the components page of the Vintage-Trek website.