I suspect that you are just seeing manufacturing tolerences. As long as they both fit the hole there would be no reason to reject the thicker one as it would serve its purpose just as well and possibly better than the thin one which I can see though would look neater.
These sort of low tech parts were often sub-contracted out to very small companies and I have seen a lot of variability in production of such parts from the UK, Canada and Australia.
Of course you are quite right, it could just be a verson for a better armoured vehicle.
David
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