I think you're overestimating what Winston's task would be. He's asking the question of if the past was better than today. Now, he has some of today to look at, how today operates.

By talking to this old man, he can use those stories to compare and contrast. He's gotten that Oceana's textbooks are inaccurate, in this, just in the old man's recollection of top hats. He's also got the recollection that a drunk man picking a fight with a wealthy capitalist may receive nothing more than a bit of a shoving for punishment.

He's not writing a book. He's just looking for clues. The clues are there if he's interested enough to look for the answers, rather than want them handed to him.