Now I have proof of this Mk I rifle connection. First you must read the attached page from BRITISH ENFIELD RIFLES Vol. 1 by Stratton, Charles R., ISBN 13 188239131-8 3rd edition. It describes and shows the drawing of Mk I Lee-Enfield. If I understand it correctly, there is only half of standard charger guide on the left present AND it also moves forward when the bolt is pulled all the way back (open position). Therefore an extra bump on the charger itself is supposed to give human fingers more stability and guidance on the right, which is the least stable half of the charger, left being contained and supported by the charger guide.