I picked this up from a listing that said it came from an estate sale and appears it came from the original owner with box, guarantee and even a little gift card. It is in pristine condition and the band is in great shape and looks to be original. It has a 10KGP bezel and stainless back.
For the ID, I am thinking Co-ed "A" based on the band and the ads. However, there are ads for Janet and Marie that look very close. In some ads you can see Janet has etching on the case and I came across one on eBay that I will post in the comments with the owner's permission. Marie also seems to have etching on the case and different lugs in a close up I found. In some ads they look identical to Co-ed. Will look forward to hearing what you all think. Thank you!
A photo showing the band and other items that came with it.

And a Janet ad showing etching detail. And Marie showing detail.

Full 1948 Ad

Hey Kathy, Janet and Marie are close, but no cigar......I think you nailed it with Co-Ed "A" right down to the original band. I love finding them like this in the original box with paperwork. A lucky score! :o)
Sometimes the outer cardboard box lid is end stamped with contents ID, is this the case this time?
In reply to Hey Kathy, Janet and Marie by neetstuf-4-u
Thank you : ) No unfortunately there is no writing or stamps on the box at all. The only thing added is the name of the jeweler on the guarantee.
I'm certainly in agreement with a 1948 Bulova Co-Ed 'A' being the yellow gold version. The dial is in wonderful condition.
In reply to I'm certainly in agreement by mybulova_admin
Thank you. I took a chance with it because the photos were not very clear in the listing and was happy with the condition when it arrived : )
1948 Bulova Co-Ed "A" is good vote
In reply to 1948 Bulova Co-Ed "A" is good by jabs
Thank you : )
I still have not figured out the differences between the three, as the characteristics are not always consistent. I am good with Co-Ed 'A'. Nice example!