I think I'm done now.  I implemented the lot/sequence number last night, and just sent Casascius the link to my latest code.  Something I maybe should have mentioned to him, is that the performance in Firefox is pretty bad (3x slower than Chrome.)  I'm not sure if the JS engine is just that much worse, or if I'm doing something dumb that's slowing me down.  So maybe performance could use some work, but all test cases are passing.