Resolution and tailing factor: real acceptance criteria

Resolution and tailing factor: real acceptance criteria Writing it up because I had to work it out twice and would rather nobody else did.

I would like to understand what this number means before I repeat it anywhere.

A Janoshik report on a tirzepatide lot gives 97.7% purity. The supplier certificate for the same lot states 98.6%. Both documents name a reversed-phase method; neither states the same gradient.

My question is not "who is right". It is: given that those two figures were produced by different methods, what is the largest difference I should expect from method alone, and at what point does a gap stop being explainable that way?

the opening post answers the question as asked. The question underneath it is different.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

On integration: where the baseline is drawn matters more than most people realise. On a clean chromatogram with well-resolved peaks the choice is inconsequential. On a chromatogram with a trailing shoulder or a rising baseline it matters. Differences of one to two percentage points between defensible integrations are ordinary.