Star Trek: 10 Things You Need To Know About The Lost Era
2. Data's Lore
When everyone thinks Data has exploded in The Most Toys, Wesley and Geordi start going through his stuff. In the desk in his quarters, they find his collection of medals, "some of Starfleet's highest honours," as Wesley puts it. What's fascinating about Data is that he must have accrued most, if not all, those medals before his service aboard the Enterprise-D.
Data was activated on 2 February 2338 according to his personnel file in Conundrum. Lore came first, but not before B-4. One of his brothers had failed most evilly, and the other lacked positronic complexity. Data just needed to mind his Ps and Qs and put some flippin' clothes on after he was constructed. Deliberately left behind during the Crystalline Entity attack, Data was found by Starfleet officers aboard the USS Tripoli in 2338 and had joined the Academy by 2341. After graduation, Data was assigned to the USS Trieste and then made lieutenant commander in less than 20 years. That's all technically canon… ish.
The Star Trek: The Next Generation novel The Buried Age, which describes itself on the front cover as a "Tale of The Lost Era," and takes place between 2355-2364, depicts the first meeting between Captain Picard (no longer of the Stargazer) and then Lieutenant Data on Starbase 20 in 2360.