Hard to say, there are many factors at play when purchasing Antique jewellery.
The positive, sometimes it’s the workmanship, difficult and expensive to recreate. Sometimes it’s the cut of the gemstones, many love wonky old cuts and Rose cut diamonds. Sometimes people want to own something with history, something that may be a “one of a kind”. Sometimes it’s the hallmarks identifying it to a desirable region or maker.
The negatives - the setting can be worn, it can require rehabbing which can be expensive. Sometimes the gemstones are chipped or abraided due to age and wear. Sometimes gems have been replaced, this can negate the charm or intent of purchasing an antique piece. Sometimes resizing the piece to fit can result in disturbance to the pattern if engraved.
Generally speaking, most pre loved jewellery is sold for a combination of the value of components (precious metal weight, gemstone value) rarity and desirability. The last two factors being very difficult to quantify in $$$ terms. Certainly there is a premium associated to genuine Georgian jewellery because of its rarity.
A “standard” Victorian era 5 stone OEC Damond ring would be cheaper and easier to find than sourcing 5 suitable OEC and having a hand cast setting made.
If the Victorian era ring becomes “less standard” ie larger size good colour and clarity OEC diamonds in an ornate ring in excellent condition it becomes more expensive than a reproduction. Likewise a modern reproduction of a Victorian setting in a machine made setting becomes cheaper than the equivalent Victorian era ring.