It's another sale with availability limited to early morning and last flight of the night.
Right, so it's just another sale.
See, my understanding would have been, on face value, that it's basically like a "rolling sale". That is, you can get sale (or close to sale, viz. competitive and not full sticker) prices all year round, without needing to rely on "on sale" bulletin emails, but it only applies to fares that are 60 days or later from today's date. This would be rather similar to, say, hotels, where, for example, IHG have Advance Purchase rates but only if you book at least 21 days in advance. This doesn't necessarily guarantee that there will be Advance Purchase rooms available, but otherwise there is a somewhat consistent price all year around as long as you book far enough in advance. A sale bulletin may avail more rooms to Advance Purchase rates, temporarily lower the rate to a promotional one, and/or - rarely - offer them within time frames sooner than 21 days in advance.
I could even believe that Early Bird was a new fare type, perhaps with more restrictions or a reduction in earning.
If this is just another sale then it seems rather lame to introduce it as what seems a new fare.
The only main things which are unusual for a sale like this is the time frame, i.e. sale on until end of March, and the travel period, i.e. 17 May (or 60 days from today, whichever is later) until end of 2016.