I know that you've sorted your problem, but this may help others in the future.
When I worked at a furniture restorers in the 1980's we frequently came across very stuck and rusty steel screws, often of the hand-cut variety. The trick to loosening them was to give them a couple of sharp smacks with a hammer on the end of a screwdriver (plastic handled of course). This tends to break the 'weld' of centuries old crud that has formed between the screw and the wood.
Obviously you would have to be very, very careful with tiny brass screws but a similar technique may help.
As others have said, a correctly fitting screwdriver is absolutely vital, whether for taking screws out or putting them in. With old style screws (with a 'shank' that has no screw thread) properly sized pilot holes with clearance are vital, and always put in and remove a steel screw first before the final fit of the brass one.
Just my tuppence / 5 cents (or whatever) worth.
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