Best to operate under the assumption your notes are being collected. Nothing to stop someone from having a relay to collect them and do with them what they wish, they could even disregard delete requests. What you post on Nostr is public for the most part.

It's also trivial to do. I ran a wot relay on a 2 core VPS with 2gb of RAM, collecting the notes from ~40k npubs. It barely broke a sweat doing that.