Mostly: Classical

[lvlamb]

Shares outstanding/market cap, yet another black hole <vbg>.

Usually, summaries of companies data will have another provider (ThomsonFN, Reuters,....) than quotes providers (Comstock, NAQ, ...).
Hence, in the summaries, the market cap will be calculated on a given quote which does not necessarely is updated, be it delayed.
Market cap can be based on last close, week's average, or worse on the quote of the date when the number of shares outstanding has been revised.

Hence it is up to the sites to, whether diffuse the market cap "as is" received, or negate the market cap and diffuse a calculated field shares out * last quote.

Further, it is up to the exchanges (which in NA are self-regulating bodies) to accept or not the last filings, or to correct those filings as they wish (options, cash in lieu, rights,...).

Part of an answer in this definition from the NASDAQ:
Shares Outstanding
For NASDAQ-listed securities, the number of issued and outstanding shares for the specified security as used by NASDAQ in the calculation of NASDAQ index values. The number of total shares outstanding used by NASDAQ for index calculation reflects the value most recently reported for the security by the issuing corporation, via required SEC filings or other communication with NASDAQ, as adjusted for any corporate actions such as stock dividends. However, use and display of a newly reported value may be briefly delayed pending review for accuracy and/or the facilitation of the management of the indices. Also, values for certain non-U.S. securities may not include all shares globally issued and outstanding.

The TSO for OTCBB companies can be found on OTCBB.com, under the "Company Profile" section. Please see the following example.

The TSO for NYSE and Amex companies is provided by Reuters. Reuters uses the Quarterly Diluted Weighted Average Shares, as filed with the SEC.
http://www.nasdaq.com/reference/glossary.stm#SharesOutstanding

This morning's market cap of SSRI:
Yahooo 590.55
Moneycentral 582.55
NASDAQ 515.946

Yeah! Have fun! ROFL

FWIW, there is no longer access to ThomsonFN, "Full Report" can be accessed via Kiplinger http://tfn.kiplinger.com/index.php