This will depend on the group of people you RP with. The game developers have said that everything in-game supposedly takes place in the same year of 2E 582 so as to not put pressure on RPers by forcing them to advance the age of their characters, etc.
Obviously it is difficult to imagine all the events of ESO (Vanilla+DLCs+Chapters) occurring in the same year so the general consensus among most RPers is that when a year passes irl a year also passes in-game, making the current year 2E 587 just as you said. Of course this does require us to ignore the fact that several in-game days pass in the span of one irl day, so it might be more accurate to say that one irl year corresponds to several in-game years, but for the sake of simplicity most will stick with 1 irl year = 1 in-game year.

Problem is, the devs keep advancing the timeline. If you do Chapter content, you hear about events in the original Alliance story lines as happening in the past.

I feel like they should finally drop this vague "it's all happening at the same time even though the in-game dialogue clearly states it already happened" and focus on a coherent timeline.

Yes, new players want to try the new shiny things, but they also suffer from this vagueness. New players are not ignorant, they see that sometimes the story progression is out-of-place. If you start in Summerset, there is no point to Clockwork City anymore.

Maybe it's too late for the past DLCs and expansions but I hope the new story arc that will kick-start in 2020 will be more restrictive when it comes to this. I hope it is something related to the Three Banners War (that could even give us an updated Cyrodiil PVP map). We need progression. We need to see that time has actually passed and our accomplishments were not for nothing.