I wouldn't use an expired insulin, even if it had been stored in the fridge.
Having said that, I am lucky to live in a country where the government pays for my insulin. If I had the choice between no insulin and expired insulin, I'd probably use the expired stuff. But as a T1 I'd be dead pretty soon without it so I'd be off to A&E if my blood tests showed my insulin wasn't working and I couldn't access new insulin from my GP or pharmacy.
Obviously it doesn't magically go off 1 day past its expiration date. The manufacturers guarantee that it's fine (if stored correctly) up to its expiration date. After that, they make no promises...
I've got to say that 6 months is a long way past the expiration date, though?
I’d second the suggestion of trying it and seeing if it’s lost potency. You should be able to tell soon enough. General recommendation from doctors on most meds is six months after exp. date.
I’ve used OOD insulin by accident and didn’t even notice, I have learnt to rotate new with old in fridge, I tend to have a box left when new stuff arrives so was just putting in fridge door in front, then using that, I noticed it was well out of date but think I was on last pen, can’t remember how long but remember it was well old, probly six months. Now I always tuck new boxes behind old.