Some bits of criteria to add to the confusion are: What do you have as an educated vision of the car as it would have looked after the number of decades of use and type of care it would have had and the places it might have travelled (long trips, family use close to home, dusty environment, city environment,etc)? In other words, what kind of stories does the car have to tell? Where did it go and what did it see and experience at the hands of its drivers? What kind of personalities drove and occupied the car? What kinds of conversations took place in it? What were the hopes, dreams and accomplishments of the owners and occupants? Keep in mind it would have had some maintenance and replacement of small parts like water pump, head gasket, and maybe a bearing adjustment that would have left the pan cleaner than the rest of the engine with a new gasket. It may have had a small collision that left a dent, scrape or an obvious repair, or a repetitive injury.Lots of layers of hardened dust and lube will be built up on the rod ends, spindles, transmission, diff gaskets, engine block, and depending on how much blow-by it produced, how many layers of petrified oil and dust are on the firewall and insides of the hood panels. The old oil in this mixture was refined no telling how many decades ago by people who had life stories to tell and the dust wants to tell its stories, too. All the personalities that touched it, service station attendants, mechanics, etc. contributed to its personality. It seems to me that an important consideration would be to keep the extent of cleaning and restoration consistent, and possibly, minimized. The type of wear will tell much about its previous owners' physiology and personal habits. That's why I think, in many cases, it's tragic to restore and erase all of that including the assembly and paint applied by long dead personalities. After enough more decades, the regretable firewall crud removal will have an old story to tell, also. Come to think of it, you may be able to take some used motor oil and mist it on the firewall, then throw some dust on it and repeat that process every time it starts to harden, and "restore" the firewall to its "correct" condition. Anyway, my opinion is that it should indicate a certain date at which its career ended/owner changed and it went into storage, so that when people see this bonafied time machine now and in the future, they will be able to read its history and hear its stories from observing the evidence.