To my way of thinking that sort of changing of the rules is a relevant structural change, so my point stands. In any case, those people should show up as unemployed in house-hold surveys if they're looking for jobs. But unemployment stats certainly have highly limited uses - they're really only short-term measures.

Employment rates have their own problems, but they're useful as a spectrum of measures that tell you something about the labour market.
Is the higher US employment rate among older workers a good thing or a bad thing? Why? Is taking early retirement inherently a bad thing?

Employment is ill-defined as well: when is someone considered employed?

There is no single statistic that allows us to carry out comparisons between differently structured local economies.