The information came from the registry office.
Ah, okay. Unfortunately, that means absolutely nothing when it comes to your visa, because the registry office has no way of knowing whether your visa has been processed or not.
If you gave notice to marry before applying for the fiance visa, then the permission to marry will likely be based on her not having applied for a visa yet, but they are allowing the registry office to marry you without any further investigation once the visa has been granted and she has arrived in the UK... whenever that may be.
I would say it is extremely unlikely that you will get the visa in time to marry on the 24th, given that not even priority applications sent in at the same time as yours have been processed yet... and non-priority visas generally take double the time of priority.
They added they assumed this meant the visa had been approved and I would receive confirmation in due course.
Yeah, I don't think they understand how it works unfortunately. Given Sheffield only acknowledged they had it at the beginning of this month, I doubt your visa application has even been looked at yet.
She has been applying from the US, not as a visitor, and we received the application received email at the start of this month.
Okay, so your business day count for processing should start from the date you got that email (we think - that's how it always worked before the changes).
So, if that's the case then you're on approximately business day 8, maybe day 10, at the moment. Going by recent months, priority applications have been taking 20-30 business days (though could be longer now), and non-priority have taken 50-60 business days.
I'd say best case scenario is that you might get the visa sometime in December (if the business day count actually starts from when New York received it and not when Sheffield emailed), and worst case you might not get it until sometime in February (if it takes 60 business days and the count starts from when Sheffield emailed this month).