Try looking through the corrector plate, at the primary mirror. Does the mirror appear to be brighter/clearer when looking through the cleaned (Zeiss) portion of the corrector or when looking through the still-coated portion of the corrector?
If it's brighter through the cleaned (Zeiss) portion of the corrector, then the remaining "coating" (regardless of what it is) is causing more harm than good and performance will be enhanced by cleaning the rest of the corrector plate using the Zeiss product.
The colors (brownish and grayish) of the film layers on your corrector plate don't look like those from any low-reflective coatings that I've ever encountered on astronomical telescopes (blueish - purplish - greenish).
You mentioned that the cleaned (Zeiss) part of the corrector was more reflective than the still coated part. That, to me, would be another indication that it wasn't a low-reflection coating that was removed. Such optical coatings tend to be just as highly reflective as uncoated glass, but only at selective wavelengths (colors).
My current "best-guess" is that the coating that was removed was residue from some type of fine smoke or chemical(s) that the scope had been exposed to -- perhaps on two different occasions.
What does the reflection of a white light bulb look like (intensity and color) from the cleaned (Zeiss) vs. still coated portions of the corrector plate?
What He says!!!!!!!!!