The current numbering scheme is alphabetical according to the day you were admitted--there being frequent swearings in en masse, in my case in the Opera House well before the fat lady sang there for the last time. I was once on a case with the nice fellow who has the number immediately before mine, which was neat in a minor sort of way, though we never filed any joint pleadings.
But there are some attorneys older than me who have really low numbers out of sequence. I sent an email to the State Bar asking them how the numbers are assigned, but have yet to receive the favor of a reply. Do some Washington lawyers have the recycled numbers of dead lawyers? How Gogolian. Don't try to tell me that lawyers don't have souls, now.
The state bar unhelpfully informed me today, "Once a number is assigned to an attorney it is never used again. It belongs to that one attorney." That was the entire email. No sense of history! No sense of the evolution of technology!