What happened in 1926 that made data on stock dividends reliable?

So I was able to find a source for timing around the 1926 date:

The Chicago Booth Center for Research in Security Prices

states that their initial correction for cash dividends came from:

• 1926-1936: Moody’s Quarterly Dividend Record

Since the only known complete file of this last publication was in Moody’s New York offices, the data from the earlier period were recorded in the Moody’s offices by trainees working for the research division of Merrill Lynch, Pierce, Fenner & Smith Inc.

See: http://www.crsp.com/products/documentation/data-sources

Curiously this last part appears to be a quote from 1964 article titled "Rates of Return On Investments In Common Stocks" by L. Fisher and J.H. Lorie

1964 article from the University of Chicago Journal Of Business: http://www.crsp.org/50/images/rates%20of%20return%20paper.pdf

More of a side note:

While Robert Schiller states on his Online Data page at Yale that for his book Irrational Exuberance:

Monthly dividend and earnings data are computed from the S&P four-quarter totals for the quarter since 1926, with linear interpolation to monthly figures. Dividend and earnings data before 1926 are from Cowles and associates (Common Stock Indexes, 2nd ed. [Bloomington, Ind.: Principia Press, 1939]), interpolated from annual data.

So it appears for academic purposes approximations from annual data are used for pre-1926 analysis and quarterly values for post-1926 analysis.