ADOP: How do I determine the number of old database editions?

Regarding ADOP, the docs say:

"As each online patching cycle is completed, the database will accumulate an additional old database edition. If the number of these grows too large, system performance will start to be affected. When the number of old database editions reaches 25 or more, you should consider dropping all old database editions by running the adop actualize_all phase and then performing a full cleanup."

Is there a query to determine the number of old database editions?

Thanks.