McEntarfer [0] had only been commissioner for around 18 months. The performance of the BLS in 1979 probably isn't reflective of her skills and talents.
And I'm not going to bother digging through the manuals to figure out how the BLS is calculating their standard errors, but there is a pretty decent chance they've been calculated assuming that the error mean is 0 when in fact it appears to be biased.
I can't really call it a conclusion, I just don't know if the residuals are assumed to have a mean of 0 in their model or having a mean of 0 is simply standard practice. Alternatively if you mean the appearance of bias, you can plot the cumulative sum of the revisions (first chart in the mishtalk.com link) vs. a cumulative sum of a normal variable with the same standard deviation. A clear trend emerges because the mean adjustment isn't 0.
In fairness though, Trump's decision is clearly political, these sort of technical factors aren't important enough to rate an official press release and there isn't a cut and dried case that there is anything wrong with the BLS's methods looking in from the sidelines. But for the last few years they have been too optimistic with their estimates and that does strengthen Trump's case.
And I'm not going to bother digging through the manuals to figure out how the BLS is calculating their standard errors, but there is a pretty decent chance they've been calculated assuming that the error mean is 0 when in fact it appears to be biased.
[0] https://en.wikipedia.org/wiki/Erika_McEntarfer