The measurements were finally shown to be effects of the immediate environment on the measurement apparatus.
That detectors used in labs may vary with time by >0.1%, unknown to their users, seems pretty important. How did everybody involved not know?
To make things more specific, those labs had uncertainty budget with something like 20 terms for the things they measured. Each of those terms had associated probability distribution etc. They had uncertainty budgets for all the methods they did etc., and some of those where probably dated, done by someone else, etc. etc. Who checks that? Is the check rigorous enough? Are some assumptions made that don't hold to scrutiny?
So it is actually very easy for error to creep in, I would say actually very likely.