Here are two evidences that the Commodore 1350 mouse and maybe some of the first 1351 are Neos mouses in other housings.
One of them is in this web page:
Translated to English and in
Spanish.
The translated page doesn't lets download the very big pictures(limitations of Google translator).
Observe the size of the plastic of that connector. Inside the mouse is a Neos chip MB88201, but in the underside of the board it has cuts on some tracks and added four leads that take the direct readings to the D9 connector.
Can it be a retrofitting at factory? It is a 1350 or a 1351? The first is always in joystick mode and the second has the option if you press the left button while connecting, like the MSX mouse and the Neos, but is not tested in the web page.
The other is inside a
web page that I brought here on a previous post.
Observe the same odd shape connector, and here you can see the sticker with no model nor "Made in", but serial number begining with YQ. Inside the same Neos chip, but alas, no underside view. Fortunately the owner has tested it only works in joystick mode, so it is definitely a 1350.
The main-boards are exactly the same as the Neos mouse, so can be that removing the leads and re-welding the cooper tracks they end being Neos mouses....
To probe it I've bought on Ebay one mouse exactly like those, but must wait to test this.