The documentation for EXPIRE INVENTORY command says "If you do not specify either NODE or DOMAIN with value, data for all nodes is processes". That is in fact how it works up to 6.3.6.100, but it seems that there is a bug in 6.3.6 that causes it to only expire a handful of randomly selected nodes, unless you specify "NODE=*".
Have any of you run into this? If you're using 6.3.6, I would urge you to check the expire history, i.e. select date(start_time) as date,count(*) as nodes,sum(affected) as expired from summary where activity='EXPIRED' group by date(start_time)
