In 2018 an Amazon customer in Germany made an access request under the GDPR. Amazon sent him a link to 1,700 voice recordings. They weren't his. They came from someone else's Alexa, recorded in someone else's home.
He downloaded them before Amazon took the link down. Journalists at the German magazine c't listened and worked out who the stranger was from what the recordings contained. Amazon called it "an unfortunate case of human error and an isolated incident."
What it shows
The answer to an access request is only as good as the company's own records, and nobody but you can tell whether it's yours. A mistake in the reply can expose another person entirely.
For your own record
Read what comes back. If it holds anything that isn't yours, or leaves out something you know they have, reply in writing and keep the date. The reply is a claim they've made about you, and it goes on your record like any other.