Satoshi and Shigeru knowing each other even before the events of episode one was retconned.
In the first episode they talk like they met for the first time.
Dub-only. Given the context of the pre-release material, the nuance of their Japanese dialogue in the first episode indicates that they're familiar with each other. It's certainly not how Japanese people would speak to someone they've never seen before, even in a particularly rude way.
His bio in the pre-release material leading up to the anime's launch:
「サトシの幼なじみで最大のライバル。オーキドはかせの孫だ。」
Literal
: Satoshi's childhood friend and greatest rival. He is Dr. Orchid's grandchild.
Suggesting that their past relationship and rivalry will be rather faithful to their base characters of Red and Green from the Game Boy games. Here's the first thing Shigeru says to Satoshi in the first episode, after Satoshi bumped into him:
「痛いのはこっちだ!ん...!? お前はサトシだな。はいはい、サ~トシさんだよ!サトシ君は最初から遅刻かい。」
Literal
: That hurt! Hm...!? You're Satoshi, aren't you? Yeah yeah, it's Saaatoshi-san! Is Satoshi-kun late from the start?
The dub's choice of English then proceeds to change and over-embellish the context/nuance completely, as if Gary's only ever
heard of Ash and gives Ash the honors of "meeting" him, despite that conflicting with later encounters and flashbacks. Much like a certain companion's not-so-dead mother.
"Hey, watch where you're going! Well, you must be Ash! Better late than never, I guess! At least you get the chance to meet me!"
(If the dub wasn't an inaccurate mess of a localization, this might have been better: "Hey, watch where you're going! Hm? Well oh well, if it isn't Ashy-boy! Better late than never, I guess!" Proper native English interpretation of the original nuance using localized names/mannerisms, and none of the plotholes.)