I haven't seen this in several months (and I've been watching); the admonishment seems to have vanished from the local meme selection. More often, someone links to a specific apposite post, or possibly sequence.

You may be right. I think there has been less of that lately.

It's just entirely unclear how we'd actually measure whether people who read the sequences do so before or after logging in.

I wouldn't say it's entirely unclear. I'm curious enough to start a poll.