My tyre has hollow knobs, is it normal/desirable/essential for maker to disclose? I noticed my back tyre has hollow knobs and I can't remember ever seeing this before. Some of the knobs have turned out to be hollow inside. I know YGWYPF, my questions are:


Is it normal? I got no meaningful results with google.
Is it desirable on a budget (even cheapskate really) tyre? It wouldn't
surprise me on a £££ model, but in this case my guess would be that
it would not meet the balance between extra cost of manufacturing
complexities vs the savings on raw materials.
Shouldn't the label say the knobs are hollow? My loose thoughts
would be that this has a bearing on a user's ability to assess
things like performance and remaining life? Even if it's the
subconscious visual assessment of these? I bought this in the UK but it's a global brand (and so is probably the model).


I'm aware many on here would argue this tyre is way overdue for replacement, this is not what the question is.

Edit: Clarification in response to some early comments.


I can't tell for sure if this is a manufacturing defect, it might be, but I think this is part of my question really.
The holes do not seem to go through the casing to the tube inside. The best way I can describe it is that it seems like they are hollow blocks/knobs glued onto a slick tyre. It also seems that the hollow space inside the hole is bigger that the opening that has been created.
I estimate I've ridden 100 to 1000 km on this tyre, 95% tarmac (from dry to heavy rain), 5% well compacted gravel path, very little harsh braking. Estimates are very rough because I don't use any tracking and my cycling comes in irregular spells of commuting.
They do indeed seem irregular. To me, this could equally indicate "unintended error in manufacturing" or "intended by design but poorly executed". The photos are a decent indication of the number and spread/distribution around the whole tyre. I'm fairly sure I didn't ride over enough broken glass (or similar) for that to be the main cause.
I don't think the tread blocks are 'hollow' exactly. 

Tires are made up of layers of different formulas of rubber. I think you have worn though the outer layer and a little chip of rubber has flaked out of the center of some of the the blocks. Now you can see that the next layer down has de-laminated from the outer a little, so it looks like there is a void there.

If the blocks are hollow, the void is only right at the bottom of the block, and would only be exposed if the tire is very well worn, as yours is.