do you think it possible that back in the 70's Indian Curries were not so popular as now so there may not have been a need for a Curry Base and the flavour of the 70's Curries may have been from a ' Curry from scratch method ' ?
According to Pat Chapman, "formula curries" (i.e. those using a curry base and other pre-prepared ingredients) were pioneered in the late 1940s:
"Many of our 'Indian' restaurants operate to a formula which was pioneered in the late 1940s. In those early restaurants, a way had to be found to deliver a variety of curries, without an unreasonable delay, from order to table. Since all authentic Indian recipes require hours of cooking in individual pots, there was no guarantee that they would even be ordered.So cubed meat, chicken or potatoes, dhal and some vegetables were lightly curried and chilled, and a large pot of thick curry gravy, a kind of master stock, was brewed to medium-heat strength. To this day, portion by portion,on demand, these ingredients are reheated by pan-frying them with further spices and flavourings. At its simplest, a Medium Chicken Curry, that benchmark of middle ground, is still on many menus, though sometimes disguised as Masala, and requires no more than a reheat of some gravy with some chicken"
This is from Pat's website which can be found here:
http://www.patchapman.co.uk