That might work for the recently deceased, or still living, in transitory medium such as snow; distortion of (for example) footprint castings is sometimes cited or claimed. I don’t think it’s the case with meter-wide dragonflies though. :’)
What if the fossils themselves are repeatedly being remineralised, with the most exposed parts getting more deposition than the corners and nooks, thus preserving shape?
Those dragonflies seem to delicate to be able to fly, for their size, lol!