Hi Stu, the most rear mark is an intermediate inspection mark. The one on the middle is a final inspection mark. These are often called Waffenamt Marks (Waffen=Weapon, amt=Office). The most forward is a proof mark, used to indicate the pistol passed a "hot" or over-pressure load firing.
Stu, chances are pretty good the most rear inspection is a SE/83 rather than a SE/63!