Makes perfect sense to me that a CID investigator would hold a SP/7 rank. After all, that job has no need to "push troops" or act as a PSG, most of the time he is probably working alone and in civilian clothing.
And that makes exactly TWO bonafide photos of a SP/7 that I've seen.
SP/6 was a very common rank when I first went in in 1980. In fact, in food service or medical branches, it was hard to find a "hard striper" at all. IIRC the way it worked was like this: If you had a medical section, the Platoon Sergeant or Section Leader might be a "hard stripe" E-6, i.e. a Staff Sergeant. But his job was mostly making duty rosters, overseeing training and making sure that the troops were doing their jobs.
The troops with technical jobs, though, the cooks, the medical techs, mechanics, etc, were almost always Specialists whether they were SP/4, SP/5 or SP/6.
In terms of authority, though, SP/5s and SP/6's were still considered to be NCOs while SP/4s were not. The rule was that a "hard striper" outranked a specialist of the same grade, but not of a higher grade, regardless of Date of Rank.
So a corporal outranked a SP/4, but a SP/5 outranked a corporal. A SGT (E-5) outranked a SP/5 but a SP/6 outranked a SGT, and so on.
I believe that in the original concept of the Specialist rank, any NCO would outrank any Specialist, but it didn't take long for the Army to realize that having a 2-years-in-service Corporal barking orders to a 12-years-in-service SP/6 wasn't going to work for anyone, so they adopted the system that endures even up to today where there actually are a few hard-stripe corporals out there (typically they are found in combat arms units) who by regulation outrank any SPC (the current abbreviation for SP/4) regardless of DOR.
One final observation: The switch from SP/5 to SGT and SP/6 to SSG was final by 1985 but in my experience this was a gradual thing that started years before. I don't recall ever seeing a SP/6 after about 1983. I'm sure there were some around, but I never saw them. By the time I got to Germany in 1987, SP/4 was the only specialist rank left. I was promoted to SP/4 in March of 1988 and it was later that year that our Orderly Room posted a memo that from that point on the abbreviation for the rank would change from SP/4 to SPC.
Edited by Martinjmpr, 18 December 2015 - 11:13 AM.