Salvatore,
The 1/78 on the slide is the manufacture date of the slide. These are most likely not unfired guns, but NATO maintenance guns. What I mean by that is in the late 70s through early 80s the guns went to maintenance. Older P38/P1 slides were replaced with what is known as "fat" slides. Many of these guns did not go back into circulation after the maintenance was completed. Sometimes the serial number on the frame, barrel, and slide will be different, other times they will be the same. Depending on the maintenance performed the new slide was sometimes stamped with the last three numbers of the frame serial number.
If these are the weapons I am familiar with, they are Bundeswehr P1s used by the German Border Patrol.
If it was a NATO maintenance pistol it will have either a serial number on the right side of the frame (early maintenance period), a BW or Bw on the left side of the frame (late maintenance period), or sometimes both (middle maintenance period).
If you can still get one for $349.00, do it. They are magnificient firearms.