It takes as long as the spring only because they weren't looking. They can stretch the oath that far, they can be disinterested in knowing - but now they know, and so there it is. Elwing of Sirion is twenty-three. Half-man, so fully grown. Sirion is a city of refugees. Elves and Men and, since there are Men, children. Elwing herself has infant children.
They debate whether to send messengers. Debating is allowed, even protracted debating. The Oath, these days, is loud in their minds, and louder when they're pushing it like this, but they drag out the debate for a few months. Messengers will probably be shot on sight. The last time Elwing of Sirion received news of the House of Fëanor it would have been the news that her brothers, twins, aged seven, had not survived the sack of Menegroth.
They send messengers anyway. The messengers are shot on sight. They have good armor, Fëanorian armor, and return home injured but not lethally. Maglor's songs no longer stitch them together. War makes you worse at healing. Maglor's songs are more powerful than ever - he can knock back a wave of approaching enemies, he can make a blade's next touch deadly, he can make them faster and more impervious to danger, but he can no longer do healing.
Maedhros, when he thinks about this, thinks that perhaps there needs to be part of you that is not broken for healing spells to draw on. Or perhaps the Enemy is amused to strip that away first. Perhaps the Enemy finds it suited to the theme as the Oath tugs and yanks and twists them into violence against the lands they once defended and the peoples they once sheltered.
They send messengers to Sirion again. The messengers deliver a plea for the Silmaril, an offer of anything at all in exchange. The messengers do not return at all.
The Enemy is many many hundreds of miles from here but at night Maedhros can hear him in his head. Is it so implausible that I really let you go? the Enemy likes saying. You serve me better free than you ever would have willingly.
The Oath allows them to work slowly. They begin planning the sack of the refugee camp even more slowly than the Oath allows, so slowly that its currents are constantly tugging at them. Any slower and the currents would erode all the things they care about which are not the Oath, and it would be a disaster to go to Sirion once they've been stripped of their capacity to care about anything that is not the Silmaril. So they do not hold out forever. But they work as slowly as they can.
Blink. "I haven't been introduced to most of them. Uh, I told Maedhros once it was safe to introduce himself to fairies that way because it didn't overlap his real name which is Maitimo?" It clicked when Sauron said it.
"Maedhros is you?" Fëanor says to his eldest son. "That's not a responsible translation. ...so names you parse normally, and they're heard exactly as you said them, and you say them exactly as you initially heard them, just like everyone else does for all words. Everything else, the superposition of sounds. Which we'll run tests on later once you've deposited our foes in a black hole and - hmm, there's a lot else to do. If we go to Eru's other projects via travel through the stars it'll take us a very long time...how do I build you a gate back to Fairyland? How are gates generally built?"
"Gates are generally built with sorcery. It doesn't work outside Fairyland. So I have no idea how you're going to do it. Are we sure we don't want Melkor and Sauron for anything? I think the black hole is a one way trip."
"I didn't actually shake them down for information. I don't know where the Silmarils are right now but probably in there somewhere."
"I'd like to talk with them," he says, "if you don't mind and think it's comparatively safe. The Valar and Maiar know a lot of things we'd otherwise take a very long time to learn, and while we are not pressed for time I understand it that there are still griefs elsewhere in the galaxy, and evils in your home world." He starts walking. Everyone except Maedhros and Fingon follow him.
Promise glances over her shoulder at them, but follows the party to the fortress. "If all I let them do is talk it's safe, I'm pretty sure I won't screw that up."
"Um, we're more immortal than you are - although I don't know all the details because I've never been reduced to parts too small to eventually regenerate or known anyone who was - and most kinds begin spontaneously but there are some breeding kinds, and every kind has its own innate magic and other properties, and we're all winged humanoids?"
"No, sorcery's learnable but kind magic isn't. My kind is leaflets and leaflets are each immune to one kind of sorcery; my name can't be learned by sorcery but another leaflet might be immune to being turned into an animal or something. And it isn't very useful in my case since mental sorcery is hopelessly obscure anyway and not a prominent way to get a name. I also have a tree which has special properties, but that's more a property of the tree than me."
"Conventional ways are being told by the fairy belonging to the name for whatever reason, or someone else who has the name, or being the Queen. The Queen is a one-of-a-kind fairy whose kind magic is knowing all other fairies' names. Leaflets are all female, all close to my height, all have leaf wings but it can be whatever kind of leaf, and when we haven't recently been set on fire and raided orc wardrobes we tend to be found in outfits made of leaves. Coloration and such might differ but no leaflets are going to glow in the dark or have antlers or anything."
"Glowgolds glow, most strikingly in the dark. That's not their kind magic, they just glow."