So I've dropped a BIG error here.
I've used the "Remove fields except..." action on my whole library.
Not a problem so far - I set the exceptions to suit.
BUT - I did NOT realise that Remove fields except also strips out the artwork!
I thought except %_covers% or just _covers in the except field would leave the covers in place, but it looks like it doesn't.
Can anyone tell me how I'd remove all fields except artwork?