As quietly as Microsoft defined the dates it would stop selling Windows 7, over the weekend it revised its end-of-sales deadlines again, saying it had made a mistake.

Last week, Microsoft told customers that it would require computer makers to halt sales of new Windows 7-powered PCs at the end of October 2014. Now, its sales shut-off page shows "To be determined" instead of the future date.

"We have yet to determine the end of sales date for PCs with Windows 7 preinstalled," a Microsoft spokeswoman said in an email reply to questions Tuesday. "The October 30, 2014, date that posted to the Windows Lifecycle page globally last week was done so in error."

The halt date for retail sales -- Oct. 30, 2013 -- was legit, Microsoft said. "We are confirming that the retail software end of sales date for Windows 7 did happen on October 30, 2013," the spokeswoman said.

Microsoft's practice is to stop selling an older operating system in retail one year after the launch of its successor, and halt delivery of the previous Windows edition to OEMs two years after a new version launches. The company shipped Windows 8, Windows 7's replacement, in October 2012.

The October 30, 2014, date fit that policy. If Microsoft later decides on a different OEM end-of-sales trigger, it would be the first departure from the practice defined in 2010 when Microsoft set the retail drop-dead for Windows Vista a year after the launch of Windows 7.

It's possible that Microsoft will still tell OEMs (original equipment manufacturers) to stop selling Windows 7 PCs in just under 11 months, but did not want to publicize the date now. Microsoft did not reply to a follow-up question asking whether the retreat from the Oct. 30, 2014, date meant customers could infer it would be later than that.

"We'll have more details to share about the Windows 7 lifecycle once they become available," the company said today.