No "old paint" isn't the name of my horse, it's all the old bottles left over from other projects. Some go back to the days when model paint was actually affordable.
You can see I opened the $1.69 bottle. The paint was still good so I used it on a project I was building. I mixed it with a little Roof Brown color to get a darker red. I thinned this with Diosol, the Floquil solvent, to make a stain. I broke the plastic inner seal that keeps the paint fresh. It was replaced with a small square of plastic cut from a sandwich bag.
I even found a bottle of Flo-Stain Driftwood, the elusive elixir used on a lot of FineScale Miniatures kits. The Driftwood was still good. I used one of the Micro Mark submersion mixers to get the stain back in usable condition.