A door going up around 2000 is old enough now that some panel designs have been through a few manufacturer changes - the paint color may be close but not identical, or the panel profile might be a half-inch off from what's currently stocked. We check this before the job, not during it, because a mismatched panel on an otherwise clean door looks worse than the dent did.
The other complication is hardware fatigue that has nothing to do with the panel itself. A door built when the house was new has now had two decades of openings and closings on the original rollers, hinges, and sometimes the original torsion spring. If we pull a damaged panel and find the hinge bolted to it is worn oval instead of round, or the roller stem is bent, that's a separate repair we'll flag before we go further - swapping a panel onto worn-out hardware just moves the next failure down the road a few months.