Having collected a few of these Mark 1*** rifles, there sometimes appear to be a pattern: Mark 1*** rifles with the old serial number lined-out and a new serial number with the prefix ER have very little changes performed, they are often still original even with the Mark 1 butt swivel bracket and sometimes the early buttstock.
The Mark 1*** rifles with the old serial number lined-out and a new serial number with the CR prefix often have a modified rear handguard with the backsight protector removed and a Mark 111 backsight protector installed into the Mark 1*** fore-end or else a Mark 111 fore-end is used. The Mark 111 rear sight is often used too, the nose cap almost always is Mark 1.