Each zone usually has two or more authoritative servers, listed in its NS records. Their answers carry the aa (authoritative answer) flag. A resolver only passes on what it has learned from these servers.
When troubleshooting, the authoritative server is the reference: if it returns the new value, the change is in place, and differences seen by other users are just cache effects.
Trouble starts when the authoritative servers are out of sync, for example because a secondary no longer receives zone transfers. The answer then depends on which server happens to be asked.
Example
dig @ns1.example-dns.net example.com A +norecurse