I'm in the airport, a bit bored, so I am cross posting. I had the opportunity to take pics of Campagnolo, FB and Gnutti 3-piece hubs. This is how you tell them apart.

Front hubs, left to right, Campagnolo, FB, Gnutti. Campagnolo has a bulbous end. Gnutti's end is more square than the FB end.
Rear hubs, left to right, Campagnolo FB, sorry no Gnutti. Campagnolo again has a bulbous end, and even a slight bulge on the threaded end. FB is square and while I don't have a Gnutti example, it follows suit with the front being more square than the FB.

Thanks for sharing, I'll be sure to save this post for future reference. Safe travels wherever you're headed.

Any idea when that Simplex was made?

FB did make Simplex-branded hubs. But perhaps after 1951 when FB's patent expired, Simplex started making their own. Like Campagnolo.