I'm pretty sure the Sunn Transducers were CTS, the 12's I have are for sure.
There was a a passel of speaker manufacturers in the NW corner of Kentucky, the majors were CTS and Eminence. If memory serves me, Eminence was actually started by ex CTS employees in '65-'66. I believe that they operated in a "scratch back" fashion; Eminence would help CTS with manufacturing for large CTS customers and vice versa. Same components and specs, but assembled in whatever factory had capacity to meet deadlines. It gets confusing who technically "made" what, but those old square magnet 15's are identical.
That is a common practice, for example Toyota Camrys were assembled along side of Outbacks and Legacys on one of the lines in a Subaru owned factory (Toyota owns 16.5% of Fuji Heavy Industries stock, the parent company of Subaru) in Lafayette IN from 2007 until the beginning of 2016. When Subaru demand hit the levels they currently enjoy, out went the Camrys and that line is building Subaru Imprezas going forward.
Back on point; those CTS/Eminence/Whoever square magnets are inexpensive stamped frame units, however they were pretty good woofers that saw duty in a bunch of good cabs, including being the OEM in the venerable B15 Ampeg Portaflex rigs.