It has been pointed out to me that the new Sharpe series is in fact set two years after Waterloo (ie 1817) and not in the 1790s like the books. So some of my comments were slightly out of kilter.
Sean Bean is back as the swashbuckling hero in Sharpe’s Challenge, an action packed mini-series to be shot on location in Rajasthan, India. Two years after the Duke of Wellington crushes Napoleon at Waterloo, dispatches from India tell of a local Maharaja, Khande Rao, who is threatening British interests there.
Therefore Harper can be with Sharpe no problem as can Simmerson. They are I guess part of the main story and won’t be used as flashbacks.
Also it avoids the issue of how to make Sean Bean look twenty years younger…