I don't need to know which is which, they're more or less sorted by recency. So I go through the most recent tabs and get the info I need or do the task associated, then close them, until I get back to the previous task or subject.

Sometimes I get interrupted with a new thing to look up or do, and more tabs get made and the cycle begins anew, regardless of how many already exist.

Some projects last days or weeks, and tabs related to them end up being longer-lived. If I get on one of those tabs and don't want to work on the project right then, I'll continue going back (leftwards) til I find something I can do or read in the time I have available. So I definitely have tabs that have been open for months but I do need to get to eventually.

Also, sometimes when I need to look at something I know I have (or had) open in a tab, I'll just search for it (literally, i.e. Google) again in a new tab and handle it there. Then if I do come across the old tab, it gets closed quickly.

I'm "done" when I'm back at my inbox or calendar (first or 2nd tabs, pinned). This rarely happens and when it does I'm sure there is a something in my email or a new ticket in JIRA for me to start on...

So overall it's not about knowing what's in each tab, but having a system to navigate them that works for you.