My work on the 12th Light Dragoons would indicate the use of ex-ranker officers as adjutants, regimental quartermasters, and riding masters, but also threw up several examples of such men making the transition to full combatant commissions. Indeed, Quartermaster Hammon got his cornetcy as result of the high regard that he was held in by the regiment's officers, they intervening on his behalf with the regimental colonel, Sir James Steuart, who had previously been a patron to several other ex-ranker officers in the regiment.

There does not seem to have been any expectation that these men should change regiment on commissioning; indeed, in one case Steaurt arranged things so that an ex-ranker protege promoted to a lieutenacy in another regiment would exchange back into the 12th in place of another officer (notionally a gentleman) of whom the regiment desired rid.

One man thus promoted found himself unable to meet the financial obligations of his new rank and had to resign, but the others (those who lived, anyway - Hammon was killed at Vitoria just after his promotion came through) seem to have thrived.

How typical this was of other cavalry regiments, I couldn't say.