Registry too big

Greetings. I noted KB 292726 insists that there is no limit to the size of
the registry. We make a USB hardware device; each has a unique serial #. If
we plug a series of units into a windows XP box, each time it makes multiple
entries in the registry. After approx 8 months of doing this, the registry
is too full and the only way out is to rebuild (or restore from backup). So,
if 292726 is correct, then this shouldn't happen. Yet, it does.... what am I
missing?