The RB and its companion volume the BB are a bit all over the place on dates sometimes. Generally speaking, we can observe that irons with vented handle sockets are later than those without. Likewise, those with coiled steel handles are later than with wooden. Irons whose paddles are mirror images, as opposed to identical castings, are earlier than those which are, the latter lacking the leveling pins the former required. And coiled steel handles which themselves screw into vented sockets without the need for a center eyebolt are generally later than those with.
By the mid-1930s, electric waffle irons were well into vogue, so advertisements with illustrations of cast iron models are virtually non-existent. Similarly, we can't rely on catalogs too much as stock illustrations were often used as opposed to photographs.
Although the RB and BB show Griswold and Griswold-made irons with screw-in coil handles as being variously from the 1920s, 30s and 40s, it's difficult to say with certainty circa when yours was made. There are also versions with S.R. and Co. embossed below the Best Made. Considering the vented sockets, I think about the closest we can come on yours would be to say 1930s to early 1940s.