We should check if vanilla awards these achievements on a pickup collection, or some other event. This code would award the achievement even when dropping a diamond (obtained from a blacksmith's chest, for example) and picking it up - does that happen in vanilla as well? I'd expect the diamond achievement to be awarded when the player successfully mines a diamond ore block, the blaze rod achievement when the player actually kills the blaze (but then, they still need to retrieve the rod, which is tricky)... Dunno, really.