A needle is a single-use instrument
A needle blunts on first use. Reuse is uncomfortable, and it is a documented contributor to lipohypertrophy.
Reconstitution
Page 12 of 12 of this archive, newest first.
What a 1 mL syringe does that a 0.3 mL syringe does not
A unit is a volume. A dose is a mass. The bridge between them is concentration, and concentration is a number somebody has to calculate.
What twenty companies say about storage, and what they have measured
What would make a difference is not a regulator. It is three lines on a certificate, all of which are already known to whoever wrote it.