I don't know if those spacers and longer screws are typical or not, but I have the same black rings on the mount of my monitor arm. 
Given that the images you posted of the table stand show those black rings that look exactly like the spacers I have, I'd suspect that the spacers are indeed typical if not standard. I'm pretty sure those spacers came with my monitor arm, but I got it 10 years ago so I can't say for sure.
		
		
	 
The few times I've used VESA mounts, they didn't come with those rings. I suspect they're mainly there to protect the surfaces. Anyhow, spacers would be easy to come by if needed.
	
		
	
	
		
		
			It is not uncommon to get multiple lengths of screws with VESA mounts. I guess the depth isn't standard.
		
		
	 
I've ordered that Chinese universal Pro Display XDR knockoff stand, because the LG stand is just too high for my tastes. Even at its lowest setting, the centre of the monitor attachment is at about 34 cm or so. (LG says it can move 60 mm, meaning that it can go as high as about 40 cm or so.)
That universal stand claims to go as low as 29 cm and as high as 41.5 cm. If I can get the monitor lower by an inch or two that would be great. Ideally it should be under 20", but right now the top is at 21.6" and I'm constantly looking up at the monitor. Not good for my neck and back.
		
		
	
	
 
Hopefully the stand fits. I don't know what screws it comes with it, but the screws that come with the LG 6K are 10 mm. However, it appears those standoffs add another 2 mm to accommodate that square mounting plate, and if the stand mounting plate is 4 mm thick aluminum then that would be a total of 16 mm needed.
	
		
	
	
		
		
			Any word on availability of this in the UK yet?
		
		
	 
TFT Central (which is based in the UK), has gotten theirs and has reviewed it already, last week. However, I don't see it on LG UK yet. Laptops Direct in the UK has it in their system, but says shipping is in 4 weeks.
Here in Canada, it was supposed to start shipping today, but I got mine last week for some reason.