17 week old cuckoo maran mix laying ?

[aart]

Yes, checking vents and pelvic bones can tell the tale, here' a how to:
https://www.backyardchickens.com/articles/who-is-laying-and-who-is-not-butt-check.73309/

But this is often the only way to really know who is laying what:

Sometimes you gotta catch a hen in the box to know who laid what egg.