The queen slipping through the excluder, is she a local North East mongrel ?
If so its quite regular in my experience. These tend to be darker and smaller queens which I think are adapted to our local environment. They do swarm nearly every year. Mine often slip into the super and lay 2 or 3 patches in the centre frames but then always go back into the brood box and continue as normal. Thing is you must always check the middle of the first super for brood and in particular queen cells rather than just expect it to contain honey. I have on several occasions inspected the brood boxes and found no queen cells but then found them in a middle frame in the first super.
Don't get caught out.
Cheers, Mick.