Bianchi Tange Superset 2, no oval downtube???

[Junonada]

I always assumed all Superset II tube sets had slightly larger down tubes with an oval shape at the bottom bracket. I just got a 1990 Bianchi Boardwalk that has a SS2 Tange decal but does not have the oval shape or larger DT. I had a made in Italy 95 Trofeo made with Deda tubing that had it. It looks more like my made in Japan Tange Superset 87 Volpe than the Trofeo.
So I'm perplexed.

Any ideas as to why??? Did they cost cut it out of their cheaper Taiwan made frames maybe?
I'm so confused.

 

[sd5782]

I had a Boardwalk with oval tubes. I believe it was a 1991. That one had Suntour XPress shifters if that helps pin down the year. I gave it too my nephew who still has it.