The 3.7 million page total was announced via the Chronicling America RSS feed the other day. It also said that 230,000 newspaper pages in various titles were just added to CA.
Current Chronicling America Database Totals:
“The site now provides access to more than 3.7 million searchable newspaper pages from 506 newspaper titles, published in 22 states and the District of Columbia between 1860 and 1922 .”
See Also: So Long and Goodbye! Google Is Ending Newspaper Digitization Project