First off, the whole program supposedly ends 9/25/2025, so all stickers will expire then regardless of when issued.
The color and expiration is based on when the car first had a sticker issued, not the model year. Some owners didn't apply for a sticker right away or at all, so even a 2018 could qualify. In theory such a used car should be worth more to some buyers. On the other hand, someone might have applied for a sticker for a 2021 in late 2020, shortening its expiration, so you have to ask/check (beware that some crappy dealers did that for cars on the lot, "lost" them, and didn't tell the buyer, who was then surprised when they went to apply). Here's the
Sticker issued in 2020 -- expires 1/1/2024
Sticker issued in 2021 -- expires 1/1/2025
Issued in 2022 or 2023 -- expires 9/25/2025
For example, I bought a 2019 Clarity (later sold) and didn't apply until January 2020; that car's blue sticker expires in 3 months. I then bought a 2020 Clarity, but didn't apply until January 2022, so I have a yellow sticker valid until 9/25/2025.
More info here:
https://www.dmv.ca.gov/portal/vehic...n-air-vehicle-decals-for-using-carpool-lanes/
Now, as to whether it's worth trading, that depends on a lot of factors. In October 2020, Vroom was offering what I thought was a ridiculously high price for my 2019, and at the same time Honda had $6000+ incentives on new ones and some dealers would go very low on pricing beyond that (I suspect the computerized pricing Vroom et al had didn't take all of that into account). And then with the $7500 federal tax rebate, I effectively couldn't afford to not sell the 2019 and buy a 2020 -- made around $3000 doing so. I don't think any of those conditions apply now though; it's usually quite costly to sell a late model car and buy a new one.