As an aside, many current vehicles have turbocharged engines. Many/most of those
have oil coolers and oil feed lines to the turbo and the cooler. A good bit of oil in those lines
that mixes with the new fill.
No, not even close. For instance, moly may show up on a used oil analysis, but you have zero idea which of the dozens of available moly compounds were used in the oil. Different compounds are chemically different and react with other chemical compounds differently.