I bought some second hand 716 MB irons 5-P, with CB 3,4. I've noticed on the back of the heads where Titleist is stamped, that the boldness of the letters is inconsistent on a couple of clubs. Some are thicker than others, the 8 iron being suspiciously heaps thinner than the rest. I've taken them to the course and range and they hit pretty well (8 iron included), but as I've never hit them before, I wouldn't know the difference. Is anyone able to provide some insight to this? There is also a serial number on the 6 iron, but it didn't show anything when I tried registering it.