Please note handles must include the "dot" part. For many people this will be something like "myhandle.bsky.social" at the moment, but accounts with custom domains will have something like "myhandle.mydomain.com".
Bluesky handles only consist of lowercase letters, numbers, hyphens (-), and dots (.).
With this tool you can check the history of handle and PDS (Personal Data Server) changes for a Bluesky account. In most, if not all, cases the first record will show the registration date for the account. Older accounts will have at least two records because they were impacted by the expansion of new PDS servers. Accounts that have changed their handle, because they have their own domain, or for any other reason, will have multiple records here, showing these changes.