Why "add 2 mL" is not an instruction

The question in the title: Why "add 2 mL" is not an instruction I will give what I have already checked below so nobody repeats it.

Practical question with the units stated, because I have seen how quickly these go wrong without them.

I have a 10 mg vial of semaglutide and I am working to a 2.5 mg step. My syringes are U-100 insulin syringes, 0.5 mL barrel.

I can do the arithmetic and I have done it twice, getting the same answer both times, but I would like someone to check the reasoning rather than the number — specifically whether I have thought about the residual volume correctly, and whether the graduation I am landing on is one a person can actually read.

This follows the opening post rather than contradicting it.

Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile indefinitely, and no supplier claims otherwise.

I read the opening post twice before replying, because I had assumed the opposite.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile indefinitely, and no supplier claims otherwise.

The short version is the first sentence; the rest is why.

On post #3 — agreed on the reasoning, with one qualification.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

Picking up post #3: that is the part I would want checked first.

Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile indefinitely, and no supplier claims otherwise.

Noted, and I have changed what I was going to do on the strength of it.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

Reading it back, the second half matters more than the first.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

This is the sort of thing that ought to be settled and apparently is not.

Post #8 answers the question as asked. The question underneath it is different.

Preservative effectiveness is tested against a defined microbial challenge under defined conditions. It is not a licence to treat an entered vial as sterile indefinitely, and no supplier claims otherwise.

Not a strong opinion, just a consistent one.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

Do not shake. Swirl, or leave it. Vigorous agitation introduces air and shear, and neither helps a peptide go into solution any faster than patience does.

I would rather post the uncertainty than round it away.