Update Stats not updating for all the Tables

Hi All We are running Update statistics high for the whole database every night as a cron job, as our database is small of 1.5 GB. When i run the following query next day Select distinct tabname,b.constructed,b.mode from systables a,sysdistrib b where a.tabid = b.tabid order by 1 for the database, i found few tables especially the tables which has more inserts everyday , one tables has 50000 rows and another had 10000 records, have been updated 3 months ago , but for rest of the tables it shows the current date. Why only few tables not updating on the production box but the same cron runs and updates the test box???????? Any suggestions would be highly appreciated. Thanks in Advance Kalpana Pai