When yet-to-be-migrated Lotus Notes users open any Room Calendar in their mailbox using Lotus Notes Client, they are actually looking directly at a view to RRDB database which is hosted on Domino Server, so they are able to see the whole full history of room bookings, till all the way to the very beginning of this Room deployment.
On the other hand, when Migrated Outlook users open any Room Calendar using Outlook Client, there is actually no Room Resource mailbox being hosted on Exchange Server, so you are actually looking at a Room Mail Contact, because RRDB database will always be the last entity to migrate after all users have already been migrated out of Domino Server.
That is why co-existence environment is needed here, so that this Room Mail Contact is able to use Exchange Availability Service to look up at real-time for Free Busy Time information from Busytime database which is hosted on Domino Server via Coexistence Manager for Notes (CMN), whereas RRDB database is not involved in this process.
The whole objective of Free Busy Time feature is to allow users to schedule ahead in future on room bookings, but not to schedule back in time to the past, so its Free Busy Time information in Busytime database is sorted & stored chronologically, in order for the oldest records to be purged nightly up till a week ago, so that Busytime database can always maintain within a reasonable file size to run efficiently.
