When was the last time the US Standard Atmosphere 1976 was updated? I imagine due to slight changes in Earth's atmosphere or more accurate instrumentation it's been updated at least once, but also because it's understood to be a less precise model we might not have even bothered. I haven't been able to find any evidence/papers so far detailing the changes, however.
No, this model was last updated in 1976, and only differs from the 1966 model above 51km in altitude, where aircraft rarely fly anyway. There are no newer versions of this atmospheric model.
There are other models though, some of which may be newer.