The IPO date I find for the MMM Corporation is 1/13/1978 (http://www.crunchbase.com/ipo/3m-ipo--e0c82f24).
Google Finance has price data going back to that date (http://finance.google.com/finance?q=NYSE:MMM).
However, Yahoo Finance goes back to 1970 (http://finance.yahoo.com/quote/MMM?ltr=1), as well as other ticker sources.
The main concern, of course, being: How can there be published price information from before an IPO?
The Minnesota Mining and Manufacturing Company was established in 1902 as a private company. It first raised public funds around 1903 but had a limited shareholder base. By around 1929, it was reported as being tradeable as an OTC (over-the-counter) stock but it's likely that shares were traded well before this. On 14 Jan 1946, the stock was listed on NYSE. On 26 Sep 1962 it became a constituent of the the S&P 500 index. On 9 Aug 1976 it became a constituent of the Dow Jones Industrial Average. In 2002, the company's name changed to 3M Co.
It appears that the data on Crunchbase's "IPO Date" is wrong on this one.
However, there are several companies that appear to do an "IPO" and have trading prices prior. This is quite typical of early-stage biotech companies that trade OTC prior to a major exchange listing and "IPO".
An example of an IPO happening after a company became publicly tradeable is NASDAQ:IMRN (Immuron). They had an "IPO" on Nasdaq on 9 Jun 2017, yet they had been trading as an OTC/Pink Sheet stock for months prior. They also have been listed in Australia since 30 Apr 1999. http://www.nasdaq.com/markets/ipos/activity.aspx?tab=pricings&month=2017-06
Another example is NASDAQ:GNTY (Guaranty Banchshares Inc) which had an "IPO" and NASDAQ listing in May 2017. This was a Nasdaq stock in 1998, went OTC/pink sheet stock in 2005. It has been paying regular dividends since that time. Clearly the word "Initial" is subjective! http://www.nasdaq.com/markets/ipos/activity.aspx?tab=pricings&month=2017-05
