Correct term/word for bias in calculations?
I believe the fundamental notion that you're looking for is a "systematic error in the data analysis". 

A "statistical bias" would imply some sort of sampling problem which doesn't seem to be the case from your description.

An "analytical bias" would imply a different/better laboratory technique which again doesn't seem to be the case. So although the overall results are biased, you don't need to redo the experiment itself but rather reanalyze the data using the proper calculations.