Q: If controls are unstable, can they be trusted?

A follow-up question to one of the earlier Q&As:

"If multiple laboratories observe a stability-related drift in a control material before the end of the manufacturer's claimed shelf life, shouldn't this trigger a reassessment of both the assigned target values and the validated stability claims by the manufacturer?

"From my perspective, if real-world performance consistently deviates from the validated stability data, there could be implications not only for the accuracy of QC monitoring but also for the validity of the manufacturer's stability claims."

If a control manufacturer severely distorts the claim on stable performance and/or stable shelf life, that calls _everything_ into question. If they are willing to mislead about one aspect of their product, why wouldn't they mislead about other aspects as well?

However, one instance of a stability-related drift is probably not enough reason to go nuclear on the manufacturer. A pattern of poor stability, yes. Consistent, consecutive issues, yes. Is it a problem with a single control lot? Or every lot the manufacturer produces?

However, I think the experience that manufacturers (both control and reagent) slightly inflate their stability claims is so pervasive that it's unwillingly tolerated. Small stability issues are often accepted as normal, or as inescapable. No one is perfect. Particularly in areas where the logistical chain means there is a significant time lag before the material finally reaches the laboratory. But determining when "small" actually transforms into significant is not always well defined.

In the worst case, you have to prove that the issue is control-related, not method- or instrument- related. And then get rid of those controls if there is a viable superior option. Switching to different control materials is not easy, but it's definitely easier than switching instruments.