The Ship of Theseus is a thought experiment about whether a ship that has slowly had all of its parts replaced is still the same ship.
My core tenant, Never Rewrite, raises the same question. If you replace your system, one line at a time, will you eventually have a new system?
When the last line of code from the original system is gone, is it the same one or a new one?
Does it make any difference to your customers?