Can anyone recommend the most reliable permanent security ID for a very large database of US stocks (all historical Russell 3000 members back to 1994). I just manually stacked over 800,000 records from bloomberg. anyway they have correct SEDOLs on many obsolete companies but when i pull in Factset's "Permanent ID" on those SEDOL's i get bad identifiers that point to active securities. I don't know who to trust more, but in any event i really need to lock in the best identifier possible as a standard before i start building. it's paramount that i have as little survivorship bias in by data as possible. Stat of the day...If you go back to January 1995 and get all the as-of members (securities) of the Russell 3000, 75% of them are no longer active today.