Did you know? Yesterday was the 25th anniversary of the web, according to Facebook! Happy birthday web! Except the web’s dad – who was there when it was born – disagrees.

Tim Berners-Lee (@timberners_lee) Who on earth made up August 23? #getitright https://t.co/k76dhmjlNF

Tim Berners-Lee didn’t invent the web on the 23rd of August, as Facebook (and the many, many, many organisations who wrote their own versions of the story to get some of that sweet, sweet Facebook traffic) would have you believe.

In fact, if Facebook had asked Berners-Lee, he’d probably have told them what he’s been telling people for years: the web’s 25th birthday already happened, two years ago. “In 1989 I delivered a proposal to CERN for the system that went on to become the world wide web,” he wrote in 2014. It was that year, not this one, that he said we should celebrate the web’s 25th birthday.

But wait! Facebook was very careful with its language: it didn’t say this was the 25th anniversary of the web’s invention, just of the date the web “opened up to the world”. So surely that’s accurate?

Well. The web did open up to the world in August 1991, it’s true. For the first two years of its life, it existed first as a mere proposal, and then as an internal project only available to those within CERN. It took that long before Berners-Lee decided to share it with the wider net, on the Usenet newsgroup alt.hypertext.

Unfortunately for Facebook, he did that on 6 August, in response to a request asking for research into “Hypertext links enabling retrieval from multiple heterogeneous sources of information?”

Sir Tim wrote: “The WWW project was started to allow high-energy physicists to share data, news, and documentation. We are very interested in spreading the web to other areas, and having gateway servers for other data. Collaborators welcome!”

As for the 23rd, no one really seems to know where that date came from. It first appeared as the anniversary in 2013, and is usually cited as the first day “new users could access” the web. Which doesn’t seem true, and isn’t backed up by any of the people who were actually there at the time.

Still, not everyone is poking fun: the Web Foundation, the body set up by Sir Tim to promote the healthy life of the web, is just grateful for the attention. “Many people have been asking us: Is [the 23rd] actually the right day to celebrate the web’s invention?” the group said. Its diplomatic answer: “We think the web should be celebrated every day!”