NEW Yashica lens discovered....

I continue to be intrigued by this lens, especially after hearing from a former Yashica employee that no such lens was ever considered for production...

After looking at thousands (literally!) of images on the Web, I found an identical lens with a C/Y mount: MC Soligor C/D 28 f2.8 (49mm filter) with serial numbers starting 88****** Given the age of the Soligor-branded lens (1980s?), and given that Soligor lenses were made by a wide raft of Japanese companies, it seems perfectly possible that Tomioka built these lenses and then decided to produce a few bezels with Yashica branding to gauge feedback from the trade at a time when Yashica was opting for C-type (Compact) variations of their earlier designs.
The build quality shown on the photos of the Soligor (I couldn't get permission from the owner to show them here) is up to the high Tomioka standards and there are some very positive reviews of this lens on other web sites.

Soligor made at least a dozen 28mm 2.8 lenses, and at least 3 with the 49mm filter ring - if I can find an image of the right lens that I can post, I'll upload it.

MC SOLIGOR C/D Wide-Auto 28mm 2.8 (macro)
Except the rubber is identical the same lens, including coating, position of screws, numbers colors and position, all. In my opinion was few samples made by Soligor to be presented to Yashica, in order to get mount license.

Soligor is not a manufacturer, but a reseller much like Vivitar. Like Vivitar, they use third-party entities to manufacture their lenses. So either the Soligor lens is a rebranded Yashica, or both lenses were made by a yet to be identified third party.