Guild Wars 2

I have reached level 423 tailor with one character, and level 427 armorsmith with a different character. In both cases, although I have created the correct intricate gossamer patches and pieces (i.e. gossamer shoes), it won’t let me combine them in discovery. I have double-checked that they should create an item, but it doesn’t work. Is this because it is the Ineffable insignia? Do I need to get this recipe from somewhere else?

Yes, it’s because of the Ineffable Insignia you’re using. Those are used to make lower level gear, and the intricate gossamer one specifically makes armor with the name “Imuthi”. You’ll have to make one of the “normal” stat insignias to make exalted armor.

Ineffable insignia is for crafting level 68 armor. this armor to be exact
http://wiki.guildwars2.com/wiki/Ineffable_Intricate_Gossamer_Insignia#Tailor

exalted armor is level 80, so that insignia can’t be used