Late reply, but anyway - for reference.
Just checked my TBC (5.30) and I don't see 12.70 either.
FWIW the data will be the same as long as the version you select its newer than 12.40.
If you go 12.40 or older (or enable MS990 compatibility) you will get a .cfg-file instead of the .cal-file.
The .cfg is forward compatible and will load in the newer versions, but you will loose the connection to the GeoData-folder.
Loosing the connection to the GeoData-folder is really only an issue if you use that design as a reference for coordinate system when creating a new plane, slope or map in GCS900 (as the .cfg only has a small part of the geoid/CS) as you could run into issues with the machine being outside the coordinate system if you move to another site.
For example I have created a UTM32-DVR90-geoid design/project we load in all machines, so it can be used all over Denmark for reference when creating a design in the machine.
If you just select "Automatic" when prompted for coordinate system in GCS900, or create a new Project in Earthworks, your elevation will most like be off, because it is not linked to a geoid.