With item not as described defects, do they only appear if a case is opened against you, or are they spawned from using the item not as described option via eBay messaging?

I got a message this morning where the buyer had messaged using that option and I wasn't sure. As far as I know she hasn't opened a case against me (yet!) as that is the only correspondence I've had from her.

I have offered her a full refund on return of the items, so hopefully she doesn't go ahead and open a case against me!

If I am about to get a defect for her selecting that option, how long do they normally take to show up? The one I've already got is from months and months ago and didn't even know I had got it for ages, so no idea how long after the transaction took place that it appeared.

Thanks!!