last_updated_at vs last_update

https://github.com/openid/fapi/blob/master/oauth-v2-grant-management.md contains an example:

{
   ...
   "created_at":1356123600,
   "last_updated_at":1356123600,
   "expires_at":1356123600,
   "updated_by":"client"
}

and also the normative text:

The following information about the grant may be provided:

last_updated: (optional) time when the grant was last updated expressed as a number containing a NumericDate value.
expires_at: (optional) time when the grant expires expressed as a number containing a NumericDate value.
created_at: (optional) time when the grant was originally created expressed as a number containing a NumericDate value.
updated_by: (optional) string value that indicates who updated the grant. Allowed values are 'client' and “authorization_server“.

Those two things are meant to match so one of them needs to change, I'm not sure whether last_updated_at or last_updated is the intended one.