We had a customer drop off a '65 Mercedes 220 SE that had some previous floor "work". As you can see, the owner wasn't too pleased with the quality of what was done.
Here is the previous "work"...I understand that it all gets covered with carpet, but...
Everything had to come out. The owner actually was able to find replacement panels that made it a bit easier. However, with most patch panels, they are not quite big enough.
As with most floor repairs, it is always worse than what it first appears.
All patched up as close to original as we could make it for the budget we we given.