[Harven]

Hey,
I think the skillIndex is dynamic so with one character it can be 2 but with other - 1. It's that way because:

for skillIndex=1,GetNumSkillLines(SKILL_TYPE_GUILD) do
    d("Name: "..GetSkillLineInfo(SKILL_TYPE_GUILD, skillIndex)
end

So if you're only member of the Mages guild, then the guild skillIndex is 1, but if you're only member of the Figters guild, then the guild skillIndex is also 1. Looks like the only way is to check the skill name.

When your addon is loaded you can do:

local magesGuild = 0
local fightersGuild = 0
local undaunted = 0
 
local function SetGuildIndex(skillIndex)
    local guildName = GetSkillLineInfo(SKILL_TYPE_GUILD, skillIndex)
    if guildName == "Fighters Guild" then
        fightersGuild = skillIndex
    elseif guildName == "Mages Guild" then
        magesGuild = skillIndex
    elseif guildName == "Undaunted" then
        undaunted = skillIndex
    end
end
 
for skillIndex=1,GetNumSkillLines(SKILL_TYPE_GUILD) do
    SetGuildIndex(skillIndex)
end

Of course you should use localized names instead.

You must also remember that you start without any guild skill. So you should respond to the EVENT_SKILL_LINE_ADDED event, like this:

EVENT_MANAGER:RegisterForEvent("someuniquename", EVENT_SKILL_LINE_ADDED, function(_, skillType, skillIndex)
    if skillType == SKILL_TYPE_GUILD then
        SetGuildIndex(skillIndex)
    end
end)