Apparantly and somewhat unnoticed, the Microsoft Exchange Team introduced some fixes in the Exchange Mailbox Role Calculator with the release of version 6.3. This version includes the following fixes since 6.1:

• Fixed Secondary datacenter Active and Passive megacycle calculations to take into account the number of activated databases based on the failure mode the secondary datacenter can support;
• Fixed the number of Active Databases / Secondary Datacenter Server after a first primary datacenter server failure to not display #VALUE for 2-node site resilient DAG solutions;
• Improved the number of Active Databases after double server failure in the primary datacenter site resilient calculation to deal with 3 servers in the primary datacenters, as well as, when there are 2 copies in the primary datacenter.

You can consult the Exchange Team’s changeblog here, download the calculator here. Instructions on usage can be found here.