If your camera cannot read all NINE speed notches specified in the SMPTE standard, technically, you have a non-standard camera. As mentioned, there are ways of compensating. E64T is a recognized speed and balance combination in the standard.
That's an interesting way to look at it. It's actually a selling point if one's camera meets such a standard. Too bad Super-8 camera manufacturers never made mention if their cameras were SMPTE compliant or not, and probably no "official list" exists, although one should exist.
The notch situation is perhaps a resolveable issue if one has manual aperture override in their camera. The whole overexposure and underexposure issue has been dissected in confusing ways in the past.
Many times, the internal automatic meter will underexpose an image if the image includes background sky.
In filming situations where the contrast is more even, the 2/3's over exposure may not be bothersome (in my opinion) since reversal films latitude can increase in non contrasty situations.
However, the argument for slight underexposure rather than overexposure is also valid because it means the camera's lower f-stop will help produce a potentially sharper image.
One scenario where this 2/3 overexposure will be a problem is when a performer is in the foreground and lit, and the background is darker. The non-SMPTE compliant camera's automatic metering system will naturally want to overexpose the entire image already, and the additional 2/3's overexposure will pretty much overexpose the performer.
In my opinion I'd rather Kodak compromise by a 1/3 of a stop and notch the Ektachrome film to closer match the non-standard cameras so they only overexpose by 1/3 of a stop rather than 2/3's of a stop.
Since people who own the SMPTE compliant super-8 camera have more options to match the exposure more closely they probably won't have a problem with the resulting 1/3 underexposure because they will be able to override it if necessary.
I would like to think that someone at Kodak would select a range of non-SMPTE compliant super-8 cameras to test the Ektatchrome 64 film with. Run a cartridge of Ektachrome 64 through each non-SMPTE compliant Super-8 camera and see if the ideal cartridge notch setting needs to be slightly augmented.
How does this altered notching affect the better Super-8 cameras? The affect will be minimal, and ultimately quite easy to override.