It's the same storage backend between API versions but we explicitly do not carry over ACME v1 authorizations to ACME v2. This was a decision we made prior to launcing the V2 API. See the "Existing Accounts" clause of the v2 API announcement:
Existing ACME accounts from the production V1 API will work with the production V2 API. Authorizations held by a V1 account will not be usable in the V2 environment - you must revalidate your domains for use with ACME v2. Similar to ACMEv1, accounts from the V1 or V2 staging environment will not work in the production environment.
Any existing ACME v1 authorizations are ignored by the RA component of Boulder when populating a new order with authorizations.