Authoritative DNS is the source of truth
When you update a record at the authoritative DNS provider, the new value can be available there immediately. That does not force every resolver on the internet to discard a previously cached answer.
TTL controls how long answers may be cached
Time to Live tells resolvers how long a DNS answer can be reused before it should be queried again. A record with a long TTL can therefore continue to appear with its old value for users whose resolver cached it before the change.
“Propagation” is mostly cache expiry
The popular phrase DNS propagation can sound as if the new record is travelling slowly across the internet. In many cases the authoritative record is already correct and you are simply waiting for independent caches to expire.
Plan migrations before the cutover
For important migrations, lower TTLs in advance when appropriate, verify the new service before changing production records and keep the previous service available long enough to handle residual traffic. After the migration is stable, TTLs can be increased again.
Verify at more than one layer
Check the authoritative answer, then compare it with recursive resolver results. This distinguishes an incorrect DNS configuration from a correct change that is still cached.