I very much agree, and any explanation to make it fit makes Crassius look like a fraud. I chalk it up to fanservice from back in the days when ESO wasn't as good at handling lore and try to pretend it's not a thing.

Time travel is definitely plausible. You can also find Septimus Signus' book Ruminations on the Elder Scrolls which wasn't written until the Fourth Era. In ESO it has a very interesting note implying it's temporally displaced somehow:

(Note by Ancestor Moth Brother Quintus Nerevelus: Found this at the back of the library stacks behind the Scroll of Rhunen. It had obviously been there a long time, yet the printer's sigil notes its publication date as "4E 195." This is obviously a transcription error. I think.)

The Gandranen Ruins delve in Shadowfen supposedly magically attracts books from all locations and time periods according to its loading screen, which is one possible explanation for how both of these books are in the Second Era.

ITT: Plagiarism of Crassius Curio is more scandalous than the Lusty Argonian Maid.

I love it.

I'm just heard a simple idea to excuse it and its always stuck with me. Sheo is trolling people and threw that book down.

It's fan service that is canonized through its inclusion in ESO.

Imagine if society collapses and all public books are burned/data was scrubbed, then 500 years later someone releases a play called Hamlet and credits themself, and also renames themself to William Shakespeare to solidify the fraud. It's that sort of deception that ESO sort of begins to paint.

What popular story isn’t just folk-lore written down? And wasn’t the book for theatrical production, anyway? Crassus’ contribution does not have to be the story itself, but the presentation to the audience.

This is like an 18th century symphony being based on an 11th century folk-song, which probably was derived …

A load screen in Gandranen Ruins states "Tales say that Gandranen was built by an Ayleid sorcerer, a worshiper of Hermaeus Mora who so loved books that she created a series of magical halls that would attract books from across Tamriel, no matter where—or when—they were published." This is an in-world explanation for books that are technically written later to appear in Online (additionally, there's a new portion of Ruminations on the Elder Scrolls drawing attention to the book being anachronistic).

Telenger the Artificer's book on the subject matter suggests that the "Lusty Argonian Maid" is a stock character and that many of Tamriel's cultures have equivalents (after all, it's just innuendo).

It's not unthinkable that there have been many stories or plays written involving the Lusty Argonian Maid. We see that in the real world, for example, there are not only stock archetypes but similar fairy tales across cultures. And it's common for certain stories to be re-interpreted, whether under their original names or new ones.

Nothing Crassius Curio says in Morrowind actually contradicts that the story existed before he adapted it into a play, and it's not out of the question that Curio plagiarized it--he is, after all, supposed to be a bad writer ("The Lusty Argonian Maid" is apparently at least seven acts of the same joke over and over, and all the people in Vivec seem skeptical of the play's quality--"...it's probably no better than Crassius' old plays, which were awful...").

I sometimes wonder if Apocrypha is temporally displaced in a way that allowed books from one time to enter another time like an oblivionic bridge? (But I'm pretty sure it is near impossible.)