Is the REGION variable in the IHIS available for the 9 regional divisions or only available in the 4 main regions?

I need the REGION variable to have the 9 regional divisions (i.e. South Atlantic) for an analysis where I merge external policy data. The 9 divisions are available in the NHIS, but do not seem to be so for the IHIS (e.g. only West, South, etc.). Is the 9-level version only available for certain years, or are they coded differently in the IHIS from what the codebook suggests?

Thank you for your help.

According to the records and codebooks IHIS received with the data, REGION has only ever been a 4-level variable for the public use data. In the restricted use data smaller level geographies, including state and county, are available and could be used to construct a 9-level Region variable. Perhaps this is the case with the codebook you are referring to. If not, please respond to this answer with more detail on where the codebook is located and what dataset it is associated with.

I hope this helps.