This is one of the common scenarios we have seen where, for example, customer purchased BizTalk360 licenses for BizTalk Server 2009 and they are in the process of migrating to BizTalk Server 2013. During the migration process, for short duration (ex: 6 months), they will have both 2009 and 2013 environment active. In this scenario, we recommend customers to buy BizTalk360 monthly subscription license for the duration of transfer.