Can something old and something borrowed be the same item?

There is no legal or official requirement behind the rhyme. It is a folk tradition, so you have full freedom to interpret it. Combining old and borrowed is a practical and meaningful choice. A family heirloom that has been passed down, like a pearl necklace or a lace handkerchief, is naturally old and borrowed if it belongs to someone else. This can simplify your planning and deepen the sentiment, because the item carries both history and a personal connection. If you want to keep the four elements separate, that is fine too. But if you find one special piece that covers two categories, use it with joy. The same logic can apply to something new and something blue, for example a new pair of blue shoes. The tradition is about intention, not compliance. As long as you have thought about each element and given it meaning, you have honoured the rhyme.