There’s no guaranteed consistency between relays.
Imagine you’ve posted 3 notes.
The first you sent to relay A
The second you sent to relay B
And the third you sent to both relay A&B
If I looked only on relay A, I would see your 1st and 3rd note. To see all three I’d have to look for your content on both relays A&B.
#[3] has a good YouTube video that covers it well:
nostr:note1qqykurax6le6tg0mdh0p4uhzqm7w3c0ja6unvjvyq49gf92p7xasmgza3w