I’m not sure how much of an influx there was. India has had a very great deal of very basic subsistence farming for a very long time, and it still does.
In a previous job my brother, who’s a retail designer, was involved in a store design contract with a large Indian pharmacy chain. He visited quite a few times and was given an insight into the way things work in most of the country. He said he was surprised, to say the least, to be told that 60% of Indians have never seen money. The advanced parts of the country are very advanced (space programme, nuclear weapons, Nobel science laureates). The rest really isn’t.
Is your 30% figure overall GDP or per capita ? Over what period did the fall occur ?
EDIT: And while this is interesting, what’s it got to do with speakers ?
VB