My God, Jack, you must have realised that all my examples have come from technical language and not from common language. In all these examples, "retardation" would be the wrong word because it means something quite different from retard. Retard is technically in this sense a delayed onset which may result in retardation or not. A child with a retard (delayed onset) of growth may turn out to not have a retardation of growth some months or two years later. Retard refers to an effect not appearing/starting at the expected time. If there is no later acceleration a sustained retardation may result from an initial retard.

This clear technical difference may well be disregarded in common English (I regard you as an expert there). But to disregard it in technical jargon would be a mistake.

Wolfgang