Seams are more likely to
Seams are more likely to disappear with transparent glass than opqaue glass. Many opaque glasses will NEVER fuse together without showing the seam. Bullseye French Vanilla (0137) is probably the best (but not only) example of this.
For transparents, fusing together two pieces where they broke apart from each other is your best bet because the perfect fit eliminates trapped air the makes the seam visible. Gringing an edge guarantees you’ll see the seam.