In June, someone told me that Facebook planned to file for its IPO before Labor Day. Their source was a “Facebook insider.” Since then, I’ve heard variations on the same hearsay by no fewer than six different sources. Unfortunately, none of them will identify their “insiders” for confirmation. More problematic is that the time horizon always seems to be 90 days from “now” — no matter whether “now” is June or yesterday.

So I’ve routinely ignored such rumors, particularly since Facebook doesn’t face any regulatory incentive to go public until next May. Plus, I continue to think that Facebook will stay private indefinitely, so long as Congress eviscerates the 500-shareholder rule before adjourning for the year.

And now we have good reason to believe that the social network won’t file its S-1 before December at the earliest.

Sheryl Sandberg, Facebook’s chief operating officer, is scheduled to speak at the Business Insider Ignition conference at the end of November. There is simply no way she would have agreed to this appearance if she expected her company to be in registration at the time.

The SEC does not specifically prohibit executives on in-registration companies from speaking in public, but such statements come under extraordinary scrutiny. Anything that could be viewed as front-running would be off-limits, as would any company-specific comments that don’t match up exactly to the information in Facebook’s registration documents. Were she to misstate a revenue or user figure, the company would be forced to issue an amended filing. It’s the reason that company counsel generally tells in-registration execs to stay quiet, unless there is a compelling business case to speak (new product launch, etc.).

So don’t expect Facebook to file for its IPO within the next 90 days. The 90 days after that, however, are fair game.