The original half of my house was built in 1920, it's written behind fireplace mantelpiece in front room with builders name. Same bloke built next door at same time but as a mirror image. The patching is simple, I use cornice adhesive and pertile (I think that's what it's called garden pellet stuff) or cloth mesh. It's the drummy bits and loose keys I worry about. Can't get those anchor washers here believe it or not. I been improvising using a 1/4 inch bit and squeezing liquid nails up and pushing up ceiling with acro props for 24 hours. It's does OK mostly but not that happy. I'm thinking I'll get up in ceiling, pull away insulation, prop up ceiling from inside room then pour a slurry of cornice cement over keys and lathes and let it set. Pain in arse but works well and properly.
I was wondering if usa had some neat tricks that might be easier.