nothing really... it's primarily just the platform that the market makers decide to quote on... and their decision is usually based on their costs to quote and trade.
e.g. millions of trades * cost per trade
they'll go where it's cheapest.
There could be other reasons for the switch, and usually there will be a message from the exchange, or company if there is a "platform" change.
Greenshift was never a pink sheet stock. For the last 30 business days since the upgrade(2-24-11), GERS has been mislabeled by many financial websites as a .pk. This issue has now been corrected. Not even Yahoo reports it incorrectly anymore.
They were recently upgraded from "FINRA BB only"(one above pinks) to their new status of "OTCQB"(two above pinks). Here's a list that explains the different tiers and as you can see, Greenshift's venue change means it was promoted up a tier, to the 2nd highest.
"Many free financial sites do not offer OTC quotes while others frequently mislabel the tier where an OTC company is trading. For example, several thousand OTC trading symbols have a .PK tag on them when they are not, in fact, trading on the OTC Pink tier of the OTC marketplace. Investors should go to otcmarkets.com for reliable OTC market information."
This could mean the trading restriction at Ameritrade and USAA will be lifted...
"OTCQB is fully accessible to investors and offers broker-dealers an electronic trading environment. Investors can trade OTCQB securities through their preferred broker-dealers and get real-time quotes through online broker-dealers such as E*Trade, Fidelity, Scottrade, Schwab, and TD Ameritrade."
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