Whenever I load a decompiled map thats later than like, 2009, the map is missing huge amounts of textures and props. Anyone know how to fix this?
One problem might be that you are trying to open a campaign map.
Maps that are part of a campaign are not actually bought by Valve. As such, the custom assets used in these maps can not be distributed with the game. Instead, the content is packed into the BSP file.
The term "campaign" referes to events like Gun Mettle, Tough Break, The Invasion Update, or any of the recent Halloween events. What these have in common is that players get contracts to play on the newly added maps. Again, these maps are not actually bought. Instead, the creators get paid depending on how much money the corresponding update made, meaning how many keys or other store exclusive items were sold.
Campaigns have only been a thing since 2015, so I'm surprised that you mention 2009. That is pretty early on for TF2 and all the custom assets of these maps are shipped with the game.
Can you list some specific maps that you are having trouble with?