Okay, so I wasn't sure which forum to put this in, as it deals with the dating of both the TOS pilot "The Cage" and Star Trek: Discovery. Since we will be primarily discussing "The Cage", however, it seemed fair to put it in here.
Disclaimer: this is just a bit of fun speculation, not meant to be a complaint about Discovery, as I am actually super pumped for the new show. I'm just curious to see how all the puzzle pieces will fit in the end.
Memory Alpha declares in its introduction to the plot of "The Cage": "The year is 2254 - eleven years before Captain Kirk's five-year mission commanding the USS Enterprise." While this seemed reasonable at the time of production, does anyone know of a canonical statement that places the pilot in this time period? We know that Kirk is given the keys to the Enterprise from Captain Pike, which meant he was in command immediately prior to Kirk's taking over of the center seat, as I remember a quote from Kirk in "The Menagerie" stating as such.
We also know that Discovery takes place ten years before Kirk and Spock, per the trailer. Now, we never really get a concrete date on any of the original series episodes, as at the time it hadn't even been decided to set the show in the 23rd century (that would not happen until The Wrath of Khan, if you remember). But assuming that the Memory Alpha timeline is correct, then Kirk assumed command in 2265, which would place Star Trek Discovery in the 2255 time frame.
Enter Discovery into the fray. Given the fact that Kirk wears the same style of uniform when he assumes command as Pike did in "The Cage", there are two possibilities: the late 2250's/early 2260's uniform was utilized for over 11 years, and the events of Discovery take place earlier than expected, or "The Cage" must take place later in the timeline. I have heard plenty of arguments ad nauseum for the former, so what this all boils down to is, would it be so difficult to place "The Cage" sometime later in the timeline? Maybe even as late as 2264, as Pike was already expressing fatigue from command, and it would make more sense to hand the ship over to a fresh young face like Kirk shortly after such events. That way, Discovery really could take place ten years before Kirk's five year mission.
Disclaimer: this is just a bit of fun speculation, not meant to be a complaint about Discovery, as I am actually super pumped for the new show. I'm just curious to see how all the puzzle pieces will fit in the end.

Memory Alpha declares in its introduction to the plot of "The Cage": "The year is 2254 - eleven years before Captain Kirk's five-year mission commanding the USS Enterprise." While this seemed reasonable at the time of production, does anyone know of a canonical statement that places the pilot in this time period? We know that Kirk is given the keys to the Enterprise from Captain Pike, which meant he was in command immediately prior to Kirk's taking over of the center seat, as I remember a quote from Kirk in "The Menagerie" stating as such.
We also know that Discovery takes place ten years before Kirk and Spock, per the trailer. Now, we never really get a concrete date on any of the original series episodes, as at the time it hadn't even been decided to set the show in the 23rd century (that would not happen until The Wrath of Khan, if you remember). But assuming that the Memory Alpha timeline is correct, then Kirk assumed command in 2265, which would place Star Trek Discovery in the 2255 time frame.
Enter Discovery into the fray. Given the fact that Kirk wears the same style of uniform when he assumes command as Pike did in "The Cage", there are two possibilities: the late 2250's/early 2260's uniform was utilized for over 11 years, and the events of Discovery take place earlier than expected, or "The Cage" must take place later in the timeline. I have heard plenty of arguments ad nauseum for the former, so what this all boils down to is, would it be so difficult to place "The Cage" sometime later in the timeline? Maybe even as late as 2264, as Pike was already expressing fatigue from command, and it would make more sense to hand the ship over to a fresh young face like Kirk shortly after such events. That way, Discovery really could take place ten years before Kirk's five year mission.