The dates in this dataset are "decision" date, not the application date.
In that year, there was a fast forward movement in backlog of India's GC application... Green cards have a per country cap-- at the end of fiscal year, USCIS can use the "unused" GC quota of other countries for the backlogged countries. This is why you see that "priority date" for India stays at a fixed place (e.g., 2005 for EB2 India) for most of the year, and then suddenly moves forward at the end of fiscal year.
In that year, there was a fast forward movement in backlog of India's GC application... Green cards have a per country cap-- at the end of fiscal year, USCIS can use the "unused" GC quota of other countries for the backlogged countries. This is why you see that "priority date" for India stays at a fixed place (e.g., 2005 for EB2 India) for most of the year, and then suddenly moves forward at the end of fiscal year.