I had something similar. A couple of years ago I bought on old house. The previous owners did most of the work themselves from the 1960s on.
The zinc gutter had leaked for probably decades and it destroyed part of the roof structure. The roof was held up by the wooden paneling the used to cover it on the inside (70s). So the wooden paneling was actually load bearing
Actually I've found way more stuff in this house. For example at the end of the roof the tiles weren't wide enough and instead of buying extra roofing tiles, they decided to fill it with cement and pieces of ceramic flower pots.
If you go back to the early 1900s, the cladding was installed on a diagonal, which helped greatly in preventing the building from racking. Now we rely on sheet rock and plywood to provide that protection in earthquakes and wind storms.
If you ever see a house stripped down to the sticks for a rebuild, you will hopefully notice a few braces added. Not to keep the walls from falling down, but to keep them square and true until the walls are rebuilt.
It might be more of a commercial building thing than a domestic construction one. I know I've seen it in a number of videos of renovations of larger buildings, including barns. I might have the time range off. Big cities are full of 1920's constructions especially on the West Coast, and they don't do that.
My old house (~1920) had diagonal shiplap under the floors instead of plywood (but parallel in the oldest walls). That's probably more for making hardwood floors easier to install than structural integrity.
Edit: The internet says 'start of the 20th century' phased out in 1950's (plywood), and 'sometimes diagonally'.
Laying a board over a seam in the subfloor sounds like a titanic pain in the ass. Diagonal means you might have to move the nail a little. Probably also limits the amount of dust and water that passes through from floor to ceiling.
At first look it seem like someone backed into the garage door and mangled the hell out of it but on more careful inspection the roof is being barely held up by the tracks that the door runs in and is pretty near to giving up the ghost. Was just going to splice the ends of the rafters (like someone did on the other side who knows how many years ago...if it works, it works) and replace the garage door but now its looking like I'll need a whole new roof.
What really worries me is the dodgy wiring strung all across the basement which is a combination of newish wires, old cloth covered wires and liberal applications of electrical tape to splice it all together. Luckily none of the wires seem to be load bearing...
I had to do a garage roof a few years ago. The previous owner thought it would be a good idea to put a hole in the main crossbeam to attach the garage door opener. As soon as I bought the house I removed the garage door opener and put metal plates on both side of the hole bolted together.
My "fix" held for about 11 years, but apparently it very slowly weakened, creating a small divot on the roof. Which got bigger and bigger with each rain, but since I never go on the garage roof, I didn't notice.
Until during one heavy rain I got a surprise skylight!
So yeah, you probably want to fix that before you get a total collapse like I did.
The thing I learned when we fixed our old house up for sale, is that in some municipalities you need a building permit to replace a floor that already exists with a new one. In our case water damage was from a claw foot tub drain, which I had fixed but years after the problem started, so it was in the middle of the floor. The contractor ripped it down to the joists and doubled them, which does not it turns out require a permit.
The zinc gutter had leaked for probably decades and it destroyed part of the roof structure. The roof was held up by the wooden paneling the used to cover it on the inside (70s). So the wooden paneling was actually load bearing
Actually I've found way more stuff in this house. For example at the end of the roof the tiles weren't wide enough and instead of buying extra roofing tiles, they decided to fill it with cement and pieces of ceramic flower pots.