When organizations collect evaluations of law firms and make them available to legal departments, there should be some mechanism for deleting out-of-date comments. What was true three years ago may well be obsolete today. Partners change firms; associates have high turnover; firms merge and hive off and alter practice groups.
I assume reviews have a date, but readers may not remember them. Further, when scores are aggregated (“Law Firm XYZ is rated 4.3 on responsiveness”), older comments ought to be dropped or devalued. If older ratings are steadily reduced in weight, however, the calculations will be more complicated and subject to error and the methodology that much more controversial.
My point is that if collective evaluations of law firms make sense, they need to recognize the half-life of assessments and depreciate older ones by some formula (See my post of Nov. 5, 2009: collective assessments by law departments of their firms with 10 references.).