Once a visa bulletin is released, folks start submitting I-485 to USCIS. USCIS then reports back the demand on the basis of received 485s.
If they feel that at current priority date, demand will outrun the supply then they retrogress the dates to control the demand. Once new fiscal year starts in Oct, they would move forward the dates to generate new demand.
For a June 2015 PD, I expect dates to become current in 10 years from now. If you look at pending 485 chart for EB-2 India, its pathetic and this is from 2009, 2010 when the market hadn’t picked-up. I can hardly imagine how many petitions were filed in 2012 onwards when the job market was at steep increase.