ExifToolVersion has always been represented by a float, but that doesn't work well for versions ending in a zero (like version 12.60). When the JSON is parsed, the "12.60" becomes "12.6".
Alternatively--is there a "render this tag as a string" argument you can make (similar to the "render this tag as a number" assertion like "-GPSAltitude#")?
As far as the version goes, 12.60 is the same as 12.6
There is no option to change the JSON output variable types.
- Phil