Why does navigator.productSub always equals '20030107' on Chrome and Safari?

Question

According to the MDN the archaic navigator.productSub property returns the 'build number of the browser'. This probably worked in the nineties, but it's pretty useless now.

However, i'm interested in the numbers that some of the browsers return. Both Chrome and Safari always return the value 20030107, Firefox seems to return 20100101. What's the deal with these two numbers? Does 20030107 stand for July 1st, 2003? And what happened then that was so interesting?

Here's hoping someone can dig up a little web history.

Answer 1

First released as a public beta on January 7, 2003[2] on the company's OS X operating system ...

https://en.wikipedia.org/wiki/Safari_(web_browser)

Chrome is based on WebKit

WebKit’s HTML and JavaScript code originally began as a fork of the KHTML and KJS libraries from KDE,[3] and has now been further developed by individuals from KDE, Apple Inc., Nokia, Google, Bitstream, RIM, Igalia, and others.[4] OS X, Windows, GNU/Linux, and some other Unix-like operating systems are supported by the project.[5]

https://en.wikipedia.org/wiki/WebKit