More Devil's Advocate: That only tests the K antigen - a very stable structure. What about other antigens that are more likely to and are known to deteriorate over time - Lea, Leb, Fyb, to name but a few ?
The only value to testing a K- cell against a diluted antisera is to check the DAT on the chosen panel cell, i.e., it's potential to cause a false-positive. You could simply do a DAT instead.
I'm certainly not suggesting that everyone completely phenotype their Screening Cells and Panel Cells each day (or periodically). I'm all in favor of a minimalist approach to this issue, and it appears that similar testing algorithms are acceptable to inspectors.
I really just wanted to highlight the flaws in this whole concept, from both the regulatory side and that of the users. And.....don't forget.....the manufacturer's of the red cell reagents have a huge amount of stability data.