I don't have a detailed Spridget bible to reference, but it doesn't seem there were as many year-on-year trivial changes recorded. Some fuzziness between UK specs (as my general MG picture book photos) compared to US - eg we had the plate below the bumper which housed the plate lights. The B got black plate lights instead of chrome for 78my, which seems likely change for Midget at same point. One thing which seems definite was Aug 77 change to instrument panel to match B and Spitfire, with accompanying comment that B steering wheel now fitted to US cars - both these features are shown on your example. Midget ended quietly in Nov/Dec 79, so this looks final phase - there was no run-out/celebration edition.