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 UOA, 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.