High levels of preservation of just about
anything 60--80 million years old is rare and unexpected.
Tyrannosaurus Rex is amongst the most iconic of all dinosaurs. All knowledge we have of them comes from 18 known specimens. Of those, only 8 are 50% or more complete. "Sue", one of the best preserved examples, discovered in 1990, is 85% complete. The "dueling dinosaur" specimen (found locked in battle with a Tricerotops) is 98% complete, the most perfect yet found, discovered in 2006.
These finds are rare, they're often very partial, they're often distorted by geological processes. For example, Sue's skill is deformed due to movement of the substrates it was entombed in, a fabricated replica correcting this distortion is used on the mounted display at the Chicago Field Museum, the original is displayed separately.
A "perfectly preserved" specimen is one that is intact, in its original arrangement, not damaged, and not distorted or scattered over the landscape (or more accurately, across the strata in which it was buried).
Some respect for the time, processes, and good fortune involved here would be appropriate.
https://en.m.wikipedia.org/wiki/Specimens_of_Tyrannosaurus