All produced heat goes into the ambient, and must be moved out of it. Without a fan or other forced air circulation an ambient temperature of 50°C is very likely for a cooling plate, even more if covered by protective paint. And we all know how the junction temperature influences the life time of a chip, so that it's not a good idea to run it by design at its limits.
The figures in a data sheet can be interpreted in several ways, as optimistic or pessimistic, or as marketing vs. safe limits. Add production deviations, which become visible in min/max values. And there may exist hidden dependencies, like the threshold temperature of the temperature cut off.
With power semiconductors also the internals (mounting...) of a chip become very important. And who can be sure nowadays to really get the original brand, and not some cheap clone?