Each edition is reviewed by a committee of volunteers for ASNT and is revised as is seen necessary at the time.
The 2006 edition (published in February 2007) is the 12th edition and is now available.
It is important to repeat that the document is not and has never been a Standard - it contains guidelines which the Employer uses to create a Written Practice.
SNT-TC-1A is a Recommended Practice.
It is further made clear that the Written Practice created must be acceptable, not only to the Employer, but also to the Purchaser.