These ratings would change over time, so an A+ rating in 2017 would not be the same as an A+ rating in 2019. I think that is very confusing. Is a second hand A rated model better than a new D rated one? Who knows.

I find that perfectly fine. Why should an old model retain its A rating when in fact it consumes a lot of energy compared to a newer model? Just print the actual consumption on the sticker to make comparisons between older stickers and newer stickers possible.

Nobody updates those ratings, though.

That means energy efficiency rating will change by date, A rated product of last year could be different (could be better or worse) by this year's A rated product. Can't we just use "numbers" instead?

That would encourage manufacturers to lower the efficiency of non flagship models. How about just regrading every few years? Potentially add a number to the start.

That's a good point. You could avoid that problem by giving grades relative to the best product on the market, e.g. anything that doesn't use more than 10% more than the most efficient model on the market gets an A.

Regrading every year seems to be about the same as what I propose. I guess the actual numbers used for the current rating are based on actual efficiencies of the models on the market when the regulation was introduced.

Only if consumers pay any attention to energy efficiency labels. I strongly suspect that with washing machines and dryers, they simply ignore them and look instead at the other features (particularly load size and cycle timing) and the price.

Exactly. They are willing to regulate, but slowly, inefficiently, and timidly.