When it comes to Surface RT and Pro tablet sales, Microsoft (MSFT) PR has lost all credibility. Why's that? Just look at Microsoft's statements about special Surface RT price discounts and sales on July 15 -- and then fast forward to July 18, when the software giant said it's taking a $900 million writeoff for the Surface RT tablet failure. Here's the update.

As you may recall, Microsoft started slashing Surface RT prices by roughly 30 percent about a week ago. The media sensed that sales of the low-end tablet were bombing. But Microsoft put its best spin on the story, offering this quote to The Wall Street Journal on July 15:

"We've been seeing great success with pricing and cover promotions over the past several months on Surface RT in the U.S. and other markets. People who buy Surface love Surface, and we're excited about all those additional people out sharing their excitement for Surface with other people."

Really? Great success? Excitement? 

Somehow, all that "great success" on July 15 turned into a complete train wreck by July 18, when Microsoft took a $900 million charge for unsold Surface tablets. During an earnings call with The Wall Street Journal, CFO Amy Hood said, "I want to be clear: We know we have to do better, particularly on mobile devices."

Everybody with basic knowledge of the mobile market knew that was the case -- except, apparently, for the Microsoft spokesperson who was quoted about Surface success and excitement on July 15.