I will try to check this out, but the first thing that crossed my mind while reading all of this, you mention "Perhaps this is peculiar to bilbous for some reason as he is very old."
Maybe obvious, but double check to ensure he is still in a guild? If you are not in a guild, it will not show a guild name.
And as far as changing guilds, assuming you dont exploit it by stacking, if you make a sword and imprint upon it a symbol of your name and your guild, and you change guilds later, wouldn't your previously crafted swords keep the symbols they were crafted with? Unless you re-craft them, yes. (IRL as well as in PS). Tattoo a name on your arm, break up later with that person and start seeing someone else, will the tattoo magicaly change to match the new name? Nope. Same kind of thing. I dumped quite a few non-guilded sabres to harnquist when I joined my guild, simply because I wanted my guild name on my swords. And yes, I know about what I consider an exploit, Stacking them to change the guild info or names, I dont do that.
Hope this helps.