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.

If somebody has the primary source to hand I would rather cite it than paraphrase it.

A narrower follow-up, since the general answer is now clear:

How much material I am losing to dead space, and whether that explains why a 10mg vial gives me nine usable draws rather than ten?

SleepDoc_PDX 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…

Adding the part of the answer the thread has not reached. The distinction that matters is unopened versus in use. Unopened vials are stable refrigerated for their labelled shelf life and tolerate a limited excursion to room temperature. Once reconstituted, the clock is much shorter and is set by the preservative rather than by the peptide — bacteriostatic water's benzyl alcohol is what buys you multiple draws over weeks. Sterile water has no preservative and turns a multi-dose vial into a single-use one.

Correct me if the detail matters more than I have assumed.

Reporting back.

Resolved. I wrote mg, ml and mg/ml on the vial in marker and did the division in that order, and the two of us now get the same number every time.

Dr.PathRoch said:

The distinction that matters is unopened versus in use.

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.

Worth separating that from storage and cold chain, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.