Old guide links open the new address after a slug change
Change a guide's address under Theme docs and links to the old one, a section's page or a kept version included, open the same page at the new address instead of a 404. The same goes for a theme performance report's address. An address you leave stays yours: no other team's guide can take it, so the links you shared keep opening your guide.
Addresses are given to new guides without taking one that another guide left, and a team can take back an address one of its own guides left, which then opens the guide that took it.
From a customer's suggestion.
More in Theme documentation.