"It has to do with stored digital communications - as the prior messages, unless deleted - remain in your inbox, the have access to information sent/received prior to the issuance of the warrant. The same goes with text messages, electronic apps (Skype, Line, Viber, Whatsapp, etc) - anything that remains on your device is no open for their inspection. It also extends to call history, etc - anything that has stored information on prior communications on your electronic devices."
That's not called a "retroactive warrant." In fact, there is no such thing. Any warrant could specify the collection of digital data, past and present ~ which is SOP for an ongoing investigation.
Stop and think what you're implying.