The Marines went through a change in rank structure in 1962. The old rank structure (without the crossed rifles in the chevrons) consisted of pay grades E-1 thru E-7 -- Pvt, Pfc, Cpl, Sgt, SSgt, TSgt (Technical Sgt--but, usually referred to as Gunny) and MSgt. (MSgts filled the billets as 1stSgt/SgtMaj in each unit.)
The new, and present, rank structure consisted of pay grades E-1 thru E-9 adding the rank titles of LCpl, 1stSgt, MGySgt and SgtMaj--with the new chevrons with the crossed rifles.
There was a transition period where for several years, the old chevrons were still worn until the wearer was promoted. However, rank title was changed to the use of the word Acting preceeding your rank, and followed by the paygrade. For instance, a Cpl would then be known as Acting Cpl (E-3), a Sgt as Acting Sgt (E-4), etc. And so there were, all at one time, both Acting Cpl (E-3) and Cpl (E-4), Acting SSgt (E-5) and SSgt (E-6) and so on up and down the line. My suspecion: some platoon officer reccomended other Marines in Wright's platoon for promotion and higher ranks, based on their intent to remain in the Corps, and possibly, the same unit. The guy going to technical schools [Wright] was therefore passed over, with any rank or grade increase for him to be left up to those able to evaluate his eventual work in his new specialty.
We had much the same policy in my tank outfit circa 1967: those going off to technical schools didn't get promotions finalized until after they'd returned to the unit- and sometimes not then. New guys just out of stateside training units [aka *School Brigades*] didn't get a promotion until they'd AT LEAST gone through the tank gunnery course for record with us at least once, or done at least one border tour in the *Iron Curtain* 5KM zone along the East German-Czechoslovokian border with West Germany.