Nice to see you are working on the old girl, sorry to hear about and see the screen corner 'repair', there are some bodgers about out there working on cars there really are, they should be strung up
I can see that you already knew of problems in this area.
This is always the problem of buying a 'restored' car, any make, any model, it's possible to hide anything under bondo and paint. Like oui & kev says, always best to do it yourself then you know every inch of the car all over. I do feel sorry for people with a lack of skill in this area, the best thing for them I guess is to buy a good solid un-restored car, do what jobs you can and farm out what you can't to someone you have seen work from before and is happy for you to visit part way through any body restoration and see what they are doing. As we have already said there is nothing wrong with using filler as long as it is a thin skim over new or good metal.
I have some repair panels for that area if you need one sudsonic, if you do just send me a PM, I need to keep a pair for my car incase I need them but I do have a few extras available.