Certainly the most notable on TeaChat are "Shincha" (means new harvest) versions of Japanese green teas, most notably sencha. These traditionally are available only for a few months or until sold out, whichever comes first. They usually begin appearing in mid to late April, but some come out later as it is a regional thing. Further south regions come out first, further north later.
Shincha is usually produced slightly differently than the sencha counterparts as they are harvested and go through full production and packaging immediately upon harvesting.
Next, first flush Chinese greens. I usually skip the first available ones as they carry a higher price tag that to me is unwarranted. New harvest Chinese greens can be seen appearing as early as February and more commonly March ... and then most commonly April and later. It often seems the goal with these, there is a race to be the first. So, I often feel that maybe they would have been better and cheaper if harvested when ready.
And third ... Darjeeling first flush. Again, there is a race to be the first, but with a little patience you can get excellent first flush Darjeeling that is usually better priced than the very first offerings.
The key to remember, first is not mean best!!!