Savage introduced a vent ribbed double called the Trap-Grade in 1932. It is listed on the 1932, 1933 & 1934 Retail Price Lists, but is not in the retail catalogs. The Trap Grade is pictured in the 1932 Wholesale Price List --
Fox Trap Grade, January 25, 1932 Wholesale Price List.jpg
and 1933 Wholesale Price List --
Fox Trap Grade 1933.jpg
and the Trap Gun folder --
1933 Trap Guns folder inside.jpg
The Trap Grade is not in the 1934 Wholesale Price List.
In the 1935 Retail catalog they inserted text about the double Trap Grade
below the SBTs --
1935 Retail Catalog Trap Grade.jpg
The same text is in the 1836 Retail Catalog.
Both the Trap Grade and the SPR Grade appear on the 1936 Retail Price List.
February 10, 1936, Retail Price List.jpg
The only piece of Fox paper I've seen that pictures the SPR-Grade is the 1936 Wholesale Price List --
SPR-Grade Skeet & Upland Game Gun, 1936 wholesale.jpg
Both the Trap Grade and the SPR-Grade have the regular profiled Fox frame, not the flat-side. Neither appear in any Fox paper I've seen after 1936.