Board Thread:The Quarters - Q & A/@comment-23.255.224.223-20140308192301/@comment-24150802-20140310090929

It's likely that the full history storage starts only when you subscribe. The reason full history isn't available to everyone is that it would take up a lot of storage space (and hence extra funds would be needed to pay for that space). When you subscribe, your history starts being saved permanently, but that can't be done retrospectively since it isn't possible to predict which users are going to subscribe in future.