Psst, Twitter's IPO date looks to be November 15

When completing a S-1 filing with the Securities and Exchange Commission, there are some lines that are intentionally left blank until the company is ready to go public. But, it appears that one such line was inadvertently filled in during Twitter's S-1 filing.

And this slipup possibly led to a crucial reveal for the company's initial public offering: Twitter's IPO date will most likely be on November 15.

PrivCo, a private company research firm, caught onto the mistake when going over Twitter's S-1 revisions. It saw in an earlier version of the S-1, the social network made February 15 the date employees (who aren't executives) could sell their stock. Typically, these dates are set for exactly 90 days after an IPO, according to PrivCo.

"The accidental date reveals for the first time that Twitter plans to IPO on November 15, 2013," PrivCo wrote in a blog post Wednesday. "PrivCo sources -- confirmed by the US JOBS ACT regulatory timetable for IPO dates following the first non-confidential public S-1 release -- indicate that as of mid-July, they intended to go public 3 months prior to February 15."

Twitter formally announced it's on the path to becoming a public company last Thursday when it disclosed its S-1 filing with the SEC. This filing revealed a host of surprises. Not only was it clear that Twitter will be focusing more on mobile, but it also came to light that the company isn't exactly profitable.

In its filing, the social network outlined some of the obstacles that could trip it up with its plans to make lots of money as a public company. This included a slowdown in the growth of its user base, increased spam on the site, failing to make its international market more profitable, and more.

PrivCo pointed out that in the new revisions to the S-1, Twitter went into more detail about its international users. Apparently, ad revenue per timeline view in the US is $2.17 and in the rest of the world it's 30 cents. Since it's hard to make ad money from people in foreign countries, especially in the developing world, Twitter writes, "We expect this disparity to continue for the foreseeable future."

Twitter also amped up its use of the words "mobile" and "real-time." A graph made by PrivCo shows that the use of the word "mobile" rose from 91 times in July's undisclosed filing to 131 times in this most recent revision.

"As Twitter's prospectus became more promotional in successive drafts -- which some have suggested is a response to Twitter's increasingly disappointing results -- certain buzzwords have featured more prominently," PrivCo wrote. "The clearest examples of this are 'mobile,' the arena that has proven particularly challenging for Google and Facebook, and 'real-time,' which better conveys the implications of Twitter as a marketing tool."

CNET contacted Twitter for comment. We'll update this story when we get more information.