Some additional points. The XII Manitoba Dragoons were mobilized as the 18th Recce later converted to 18th Armoured Car Regt, which was recruited from three Manitoba units, the 12 Manitoba Dragoons, the 2nd Armoured Car Regt and the Manitoba Mounted Rifles. After some debate about an appropriate badge for the 18th Armoured Car it was re-designated the 12th Manitoba Dragoons. More detail about the evoulution of the XII Manitoba Dragoons can be read here
https://servicepub.wordpress.com/201...ent-cap-badge/. Even with three regiments contributing to the unit that would be named the XII Manitoba Dragoos, the majority of alpha prefix for service numbers would be MD 10.
Active service regiments, whether infantry, armoured or artillery saw a lot of change over the period they were mobilized. They initially were recruited from a particular region, but as men were promoted, transfered, or discharged, the "localization" was diluted. The army could not and in some cases did not want the regiments reinforced with personnel from the home base. This was further emphasised by the impact of Dieppe on certain regiments. The RHLI suffered heavy casualties and in terms of the recruitment area, whole communities lost most of the men who had enlisted. Senior levels of the army did not want to have battle losses impact any particular region so significantly. Not only were communities devastated, it was bad for morale and for future recruiting. A policy to diversify the demographics of regiments was used for reinforcements after that date. Additionally, some regimental areas could not keep up with the demands for replacement personnel for their unit. These factors resulted in a more random assignment of personnel to the active units.