Walter looked up both of the guns I pictured above and they are both shipped in 1935. Up through Catalog No. 51 which equates to 1934, the NIDs were shown with cocking indicators. The new style NIDs without cocking indicators were introduced in Catalog No. 54 which equates to 1935.

These Field Grades with "NEW ITHACA FIELD GRADE" marked on the barrels like this --

were introduced in 1935, in the 459xxx range. I have recorded high grade guns in the 457xxx and 458xxx range without the cocking indicators, but generally guns in that range have the indicators.