Out surfing the web for Fluorescent deals and found these "florescent" bulbs.  These look like Sylvania end caps and date code but the etch is GE.  I have some F96T12/PK that look similiar from years ago, GE etch with Sylvania caps.  How can this be?  I had also heard from one of the electrical supply houses that GE was totally out of the T12 manufacturing in the United States at least.  I wonder if this is true now?

https://grandrapids.craigslist.org/for/d/8-florescent-bulbs-box-of-15/6284744216.html

you live in michigan aswell? Omg lol ... so many michiganders.. as i've said before, i think i've counted about 15 XD

I think it is true.  That's a sylvania box too. 

It is fairly common for bulb manufacturers to borrow competitors products. I've seen GE F40 Watt-Miser tubes from the '90s made by GE, Philips, and Sylvania. In the late 2000s I remember seeing GE F32T8s made by Sylvania. I also had some Philips MH400s made by Sylvania. Sharing products isn't new, although personally if I was selling a product, I wouldn't want my name on anything I didn't make.

GE makes a lot of T12 products, so no they have not discontinued T12 production.

The real money is in manufacturing the product, marketing and distributing it costs money, so I can't see why a manufacturer wouldn't do this..

I have a few GE 3-way incandescent bulbs that were made by Sylvania.

What is the advantage of selling products made by a competing company? Is there really any?

There are dealers/resellers who have exclusive contracts with certain brands so in order to provide the dealers with what they are wanting, the manufacturer will give the dealer bulbs with that manufacturers logo on it, but made by someone else.  Perhaps in this case, GE no longer produces 3-way light bulbs or had a hold on production for whatever reason and contracted with Sylvania.