There are many items from betas left in players inventories like white staff wrappings that add nothing to anything xD
But for brick muds, i can confirm they excisted in game, i remember when dev (mike or gaile gray) was even showing them to ppl at sometime years back, after that i dont know if they been removed from ppl's inventories after they removed the artisan in shiverpeaks, but back in 2005-2006 they did excist in the game.
I resurrect this to say that I found in the Guru archive the "infamous" screenshots:
Sources (Date: Apr 27, 2008) (Time: 06:42 PM / 18:42)
https://archive.guildwarslegacy.com/04/04 The Riverside Inn/04534 Clay Brick and Brick of Mud_ Showed today, oh noes.001.html
https://archive.guildwarslegacy.com/04/04 The Riverside Inn/04534 Clay Brick and Brick of Mud_ Showed today, oh noes.002.html
https://archive.guildwarslegacy.com/04/04 The Riverside Inn/04534 Clay Brick and Brick of Mud_ Showed today, oh noes.004.html
I analyzed the screenshot and ""apparently"" it seems real despite the pixelation due the compression. The thing here is to know "how" he obtained the items if Mike or Gaile were the only ones having them. I find it practically impossible that something like this would have survived the first weeks of the game, and not just one item, but both. Why I say this? Because the pictures of both items in the Wiki were uploaded in 2007, and the post is from 2008, so even if the trade window screenshot is real, what makes me doubt is if the icon of the items could have be taken from there to fake it.
The user who posted the screenshots says that the person who traded the items told him that they dropped near The Wilds (message #13), and "near" can mean anything in this game, more when we are talking of crafting materials and not monster materials (I don't Imagine a Wind Rider dropping a Brick of Mud). I think it's totally BS, because that terrain has been exploited thousands of times and the location is precisely at the end of the map, a good excuse to send someone to the other end of the world to look for something that does not exist to waste time... but who knows.
Anyway, this is the small contribution that I have been able to get out of the whole thing. The screenshot is cut, the names are deleted, everything is pixelated, we don't even know the nickname of the player who took the screenshot and in the May 29, 2008 update the item was removed from crafters (33 days after the post from Guru), so it's a dead-end and we can only trust (or not) in what is left and the word of the people who claim that it existed and could be obtained in past times.