I imagine the only need to install older versions would be to migrate data while trying to upgrade instances to the newer versions. Is it possible to consider more number of master releases to support? as @lpm0073 said to ensure at least they continue to work. or maybe it would be easier to have one or two type of virtual machine images, with edx-platform installed, ready to use without any package installation needed which could be used to mount and to load&migrate data.