Right, but they built and sold it. No-one is forcing anyone to use the design.
There's nothing stopping me from going online right now and grabbing a design for a car, building it, doing an IVA test and putting it on the road - the original designer is dead, who would get sued in that scenario?
Alternatively, can I copy the design of an existing model, build it to the exact spec, sell it to someone else and absolve myself of all liability if a design flaw is found in the vehicle?
I'm ignoring the fact an open source design is likely to get more analysis than just about any other car on the market.