Drawing from a pen cartridge with a syringe: how the risk profile changes

Posting this under the heading it deserves: Drawing from a pen cartridge with a syringe: how the risk profile changes Everything below is what sits behind that.

Question about a metering device rather than about a syringe, because the failure modes are different.

The instruction leaflet is clear about priming and about the hold count at the end. It is silent about what I am asking, which suggests either that it does not arise or that it arises so rarely nobody wrote it down.

Which of those is it?

Reusability: some pens are single-use (throw away after one injection). Others can be reused until empty. Confirm which type you have. Reusing a single-use pen is ineffective because the mechanism does not reset.

Adding it because I spent an afternoon working it out and nobody should have to twice.

Storage instructions for a pen typically differ before and after first use, and the in-use period is the one people miss. It is on the carton.