Does quality of insulin change?

@hypohater Welcome to the forum, yes you can get a bad cartridge, just start a new one as quickly as you can, i've had a couple in the 4 years i've been diagnosed, one of mine was down to the fridge playing up, so was stored at the wrong temperature. It's one of those situations where you've ruled out different variables such as stress, exercise, illness, issues with injection site and once you've eliminated these then change the cartridge.

I have had the same problem since last week. My readings seemed to had settled after months of combinations of doses and different types of insulin. I started a new pack of NovoRapid cartridges and a Tresiba pen with Dutch writing and stickers on them and I'm back to square one as I'm unhappy with my readings again. I'm frustrated because Nothing else I'm doing has changed, just new batches of insulin. I've picked some more NovoRapid up today - I'm now going to try the Italian stuff!
This isn't anything new. I used to use the NovoRapid throw away pens before I was given my NovoPens and had those with all sorts of different languages on them. They were the worst and I noticed an improvement straight away after switching to the cartridges which were labelled in English incidentally.
I imagine all of this medicine is made in one place and then packaged for the different countries so the packaging shouldn't matter. My thought is that the medicine may not have been stored correctly at some point either in transit or elsewhere.
Maybe it's just a coincidence. I couldn't say.