1985 when you say each stock is equally valued what do you mean? each stock has an equal weight in terms of dollars invested in it? if so there is an etf that does this for the s&p 500. it is the rydex equal weight etf "RSP" designed by the author of the article i linked yesterday. if you have daily data for your portfolio then take a year or so of it and see how it varies with the RSP. you may be right in line there depending on how often each of rebalances to get back to even money in each security. you can get this data on rsp by going to nasdaq.com and calling up a chart on it. then left click and download the xcel file (or just use you current chart service). if you are right in line then i'd do a few more years and given the same result go to rydex or another etf company and market your idea to them because rebalancing 100 stocks instead of 500 stocks obviously gives you about 1/5 th of the costs and slippage.
Who said anything about flawed? I'm sure the numbers in Bloomberg are basically correct. What I'm not so sure about is that the fundamental data listed for a particular date were actually knowable on that date, since fundamental data often gets revised after the fact.