Tubing drawn from solid material is considerable more expensive than tubing drawn from rolled plate that was welded and then drawn. It is, potentially stronger and tougher, but that depends on the chemical composition and type of processing (esp. heat treatments) during manufacturing.
As the bike industry was always very competitive, my guess is that "drawn from solid stock" would not have fared well.
It is possible to make a highly reliable and lightweight tube out of seamed stock. If drawn enough times and processed properly, it would take a metallurgist to discover the seams.
So, does anyone know for sure that Reynolds 531 DB tubing started out as solid stock, or are we all guessing.
Amir Avitzur R"G Israel
BTW: I drew tubes on a laboratory drawbench, a long time ago ...