Rules for making the SDS current

• There can only be one current SDS for a substance 
• There can be many previously current SDSs linked nose to tail going back in history
• Current and previous SDSs cannot be changed
• There is (usually) one "next" SDS which is not yet effective or requires attention
• There can never be more than one "next" SDS for a substance
• If the substance changes and is saved, the "next" SDS is automatically created or updated
  
• All incremental substance changes are reflected in the "next" SDS
• The "next" SDS becomes current when:
  • All QA errors are eliminated
  • All hazards have been tagged as 'confirmed'
  • The author inserts a date for it to become effective
  • The effective date (which can be set in the future) is today or older than today
  • It replaces the current SDS
• The current SDS can have an expiry date but that is cosmetic only
• The current SDS cannot be withdrawn until it is replaced
• The replaced SDS gets an automatic withdrawn date when it is replaced
• The replaced SDS gets linked (in history) with the new current SDS