How to verify the access_token of Sign in with Apple?

I saw the description

You may verify the refresh token up to once a day to confirm that the user’s Apple ID on that device is still in good standing with Apple’s servers.

in https://developer.apple.com/documentation/signinwithapplerestapi/verifying_a_user .

I have two question about the description:

1. Why should we verify the refresh token instead of access token to confirm the user's Apple ID is still in good standing with Apple's server?
2. The doc said refresh token can only verify once a day. But i can verify refresh token multiple times in practice. Is there some conflict between documentation and implementation?

Update on 10/17/2019：

For apps running on other systems, use the periodic successful verification of the refresh token to determine the lifetime of the user session.

I also saw the description above in in https://developer.apple.com/documentation/signinwithapplerestapi/verifying_a_user . I think periodic is also conflict with once a day.

Right now, I store the access_token and set custom expires time for follow verify request. And get notification from iOS client(getCridentialState) to delete access_token.