Will a 75 dart inner fender fit a 69 dart

Sorry to hear you missed out on the inner fender.

For future reference, the inner fenders from ANY A-body will fit your Dart. '67-76, Dart's, Duster's, Valiant's, Scamp's, Demon's, Dart Sport's, even '67-'69 Barracuda's. The later stuff will have a different look on account of the charcoal canister and A/C drier, but it's just cosmetic.