Whenever you destroy a droplet it's IP address remains reserved to your account for up to a few days. The next droplet you created in the same region will inherit the IP address.

Where does DO explicitly document same?

This implied it is very short-term, speed is of the essence to get it back:
https://www.digitalocean.com/community/tutorials/how-to-downgrade-digitalocean-droplets

Step Five — Destroy the Larger Droplet to Release the IP
"... next step will almost always re-allocate that same IP address to the new and final Droplet. You should do the next step within a few minutes of completing this one..."

Step Six - Create the Final Smaller Droplet from a Snapshot
"... new smaller Droplet should have the same public IP address and the same files and data as the previously destroyed larger Droplet..."

Do nayone success get BACK the same ip? this don't work for me. Maybe i m not fast enough.