From what I can gather, Beretta began producing the 70 series pistols in 1958. The only info I can find is that the cross bolt (button) safety was replaced with a thumb lever sear block-type "shortly after its introduction". When exactly that may have been, it doesn't say. My guess would be sometime in the early-to-mid 1960s.
The 70 series replaced the Models 1934, 1935, 948 and 949. During the late 1960s they were briefly produced with a 100 series designation. During the 1970s a magazine safety was added and the pistols became known as the Model 70S. This designation replaced those of models 70 through 75, making those designations obsolete. Only the Model 76 designation was continued without the "S" suffix at the time.
The original design included the cross bolt safety, a slide hold-open device and a push-button mag release.
The series was available in calibers .22 LR, .32 ACP and .380 ACP with either 3.5" or 5.9" barrels. It was imported and marketed by J.L. Galef & Sons in the U.S. under the model name "Puma". It was discontinued in 1985.
Hope this is of some help.