Cold packs, phase-change material, and what survives ten days — does this still hold?

Asking directly, because I could not find a straight answer: Cold packs, phase-change material, and what survives ten days — does this still hold?

I have spent a fortnight trying to pin Cold packs down and I want to set out where I have got to, because I suspect the honest answer is duller than the thread this will produce.

What I have: a consistent observation across a small number of cases, collected the same way each time. What I do not have: any controlled comparison, or any reason to think my cases are representative.

The specific question is whether the pattern survives once the obvious confounder is removed. I cannot remove it with what I have.

Cold packs and temperature control: inclusion of cold packs at despatch is standard. Whether they maintain temperature through transit depends on journey duration and ambient temperature. Long journeys through warm climates put product at risk.

I would put a moderate confidence on that and no more.

At what point is a parcel genuinely a problem: if it was despatched weeks ago and there has been no update for days at customs, it might be held or lost. Days of delay at customs without update is ordinary; weeks without movement warrants inquiry.