Coming back to: Why I now write the concentration on the vial in marker

This follows the opening post rather than contradicting it.

Why "add 2 mL" is not an instruction: the powder in the vial takes up space. "Add 2 mL to a 10 mL vial" and "add 2 mL of diluent so the final volume is approximately 2 mL" are different instructions. Stating the final target volume is clearer than stating the diluent added.

If your arithmetic gives a volume smaller than one graduation on your syringe, the answer is a lower concentration rather than a more careful hand.

Add the diluent down the side of the vial rather than directly onto the cake. It is slower and it avoids the foaming that makes people think something has gone wrong.

That holds under the stated conditions and I have stated them.

Taking post #3 at face value and following it one step further.

Choosing a concentration on purpose rather than by accident: starting with "I want to draw 0.5 mL per dose" and working backward to the required concentration is more efficient than picking a diluent volume and hoping the math works out. State your target volume, then the required concentration follows.

That holds for the case as described. Change the assumptions and it may not.

A 10 mg vial reconstituted three different ways: 1 mL diluent gives 10 mg/mL, 2 mL gives 5 mg/mL, 4 mL gives roughly 2.5 mg/mL. The arithmetic is the same; the concentration determines which syringe graduations are legible.