I don't believe there is any difference between the "yellow label" Fiamme sewup rims and the "Ergal" ones, except for period of manufacture and label type.
There were yellow label Fiamme non-eyeletted 510-gram clincher rims, however, that were very different from the tubular yellows, which are a true 290-gram rim. (GEL280s don't weigh anything near 280, BTW, but I digress!)
The tubular yellows/Ergals are made from "Ergal" aluminum - 7000 series material. All other sewup rims that I'm aware of from "back then" were made from 6000 series aluminum, a lower-strength material. Ergals resist flat-spotting and "taking a set" much better than any other vintage sewup rim of anywhere near comparable weight, due to the material's higher strength, but they do also fail in fatigue occasionally. This usually, but not always, occurs at high mileage. Rider weight and riding style seems to be involved as well.
We've discussed Ergals pretty much ad nauseam here on CR - I love 'em, some other folks do too, some don't. A general recommendation might be that they're best suited for lighter riders that don't fail bike parts regularly.
Greg Parker Ann Arbor, MI USA
Where I'm still taking your cast-off NOS Ergals and "disposing" of them
> Date: Sun, 16 Feb 2003 17:24:55 -0800
> From: Jay Sexton <email@example.com>
> To: firstname.lastname@example.org
> Subject: [CR]Rims and more rims
> There is a difference between the GOLD rectangular label Ergal rims and
> the YELLOW oval label rims. I believe the Gold Ergals are the next
> generation of the Yellow labels, and are a light rim for lighter riders
> or track riding. I have heard from a number of list folks who expressed
> hesitancy about using them on the road, unless the roads were reasonably
> smooth roads. And yes, I too would love to find a set of the yellow
> oval labels. Preferably the red oval labels. Feel free to correct me
> if I am wrong on any of this.
> Jay Sexton
> Sebastopol, CA