Dream,
Volley Sight in reference to an Enfield has a very different meaning than the sights you are referring to, these were never found on the No4 rifle. The sights you are talking about are known as the Mk1 Singer, MkII flip battle, MkIII and MKIV Backsight, micrometer or aperture sights - these sights are marked to 1300 yards, not metres. Proper Volley Sights were used on No1 MKIII rifles of WW1 and were a different operation. As I stated before, the No4 rifle can be found with ANY of the MK's of backsights - this is common, normal and not unusual - it should not and cannot be a means of identifying a manufacture or factory make therefore.
Yes the manufacture data is often ( not always ) found on the left side of the receiver face. Some rifles were very poorly marked and only have their serial numbers and scant manufacture letters showing on the left butt socket face. Sometimes the manufacturing data on the receiver is worn away altogether due to wear or from being scrubbed through FTR programs - India is such an instance.
Your observation of the Mk1 vs the Mk1* is not correct ... the main difference between the Mk1 and Mk1* is the simplified bolt release cut out in the bolt way railing of the Mk1*. This cut out was a wartime expediency that eschewed the plunger bolt release of the Mk1. Furthermore the No4 Mk1* was only built by North American manufacturers, Savage and Longbranch.
Neither the No4 Mk1 or Mk1* or any type other than the No4 MkII carried the MkII trigger group, unless they were upgraded through FTR programs to subsequently become the Mk1/3 and Mk1/2. The Mk1/2 and Mk1/3 were Mk1 and Mk1* rifles that were upgraded to the MKII trigger group.
For solid information on Enfields, visit the forums in my sig.
Best, Tiki.