Adding the numbers, since they settle part of this. Practical: unopened, refrigerated at 2 to 8°C; in use, refrigerated and used within the preservative-limited window; never frozen; and a visual check every time — a haze that does not settle is a reason to stop, not to wonder.

Following on from TrialNerd_Beth — and this may be the naive question:

How to check the arithmetic without trusting a website calculator, since three calculators gave me three answers?

Dr.NateNeph said:

Practical: unopened, refrigerated at 2 to 8°C; in use, refrigerated and used within the preservative-limited window; never frozen; and a visual check…

Coming at Dr.NateNeph’s question from a different direction. Freezing is the one to avoid, and freeze-thaw more so. Ice-crystal formation and the concentration changes at the phase boundary drive aggregation, and aggregated peptide does not recover on thawing. A vial that has been frozen and thawed is not rescued by returning it to the fridge.

Closing the loop on my own question.

My error was treating units as a mass. Once I wrote mg/ml on the vial in marker and worked in millilitres first, the two of us got the same answer.

Dr.ObesityMed said:

Freezing is the one to avoid, and freeze-thaw more so.

Agreed, and it is worth saying that rounding to the nearest whole unit is usually acceptable at maintenance doses and is not acceptable at the bottom of a ladder, where one unit can be a fifth of the intended dose.