First the Stone Is a Rumor People Can Exploit
Liore · Red Stones · false miracles
Before the brothers know how the Stone is made, they repeatedly meet people willing to build power around the appearance of having one.
Cornello Shows Why a Fake Stone Is Still Dangerous
Episodes 1–2
Cornello's Stone is not the completed artifact Edward wants, but it lets him perform enough impossible-looking alchemy to build religious authority in Liore.
When it fails, the brothers learn almost nothing useful about where a real Stone is. They do learn how badly people want to believe in one.
Why it matters
The first Stone in the series is counterfeit because the story wants the audience to understand immediately that the object has social power before its actual mechanics are known.
Red Stones Keep Offering the Shortcut in Pieces
Cornello · Xenotime · Homunculi
The 2003 anime repeatedly introduces Red Stones as incomplete Philosopher's Stone material. They can amplify alchemy dramatically, but they are unstable, limited and tied to experiments the brothers increasingly distrust.
Why it matters
Red Stones prevent the real Stone from remaining an abstract legend. Edward keeps seeing evidence that the shortcut is possible before he understands what completing it would require.