I bought a "pair" of 1-2-3 blocks from one of our well know UK suppliers myself recently.
I don't know why but I decided to measure them to see if they were actually dead on 1" 2" & 3".
Imagine my surprise when I found that they were nominally correct in dimensions but were both different by up to 0.005" on all three dimensions. They were ground up nice and square, and each on its own was a nice block, but they were different sizes so in my book not fit for purpose.
I contacted the supplier who informed me they could not guarantee these were made as "pairs" and offered me a full refund.
I subsequently bought a set from another supplier on ebay for less money and they were a perfect matching "pair" and hardened as well.
It does indeed pay to check and take nothing for granted these days.
Phil