You don't want to switch code pages while processing the data unless you add extra fields to indicate code page, ISO 2022 style (or in fact old baudot shifts style)
If you were saying they lost accents outside the main 50 or whatever, I'd understand why 8 bits were a problem. But you're saying they lost accents as a general rule, right? Why did they lose accents that were right there on the US code pages? Why would that reason not extend to a 9 bit semi-universal EBCDIC?
I read the original mention as trying to claim that it could have been solved by allowance for multiple codepages.
But for processing data in one common database, especially back then, you wanted to keep to single variation - main reason for using a different codepage if you didn't work in language other than english was to use APL (later, special variant of US codepage was added to support writing C, which for hysterical raisins wasn't exactly nice to work with in US default EBCDIC codepage).
So there would not be an allowance for multiple codepages if only because codepage identifier could cut into 72 characters left on punched card after including sort numbers
