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I think the issue was that they are representing a real as a product of a rational and that more complicated type, so without a symbolic representation for 1, when representing and rational, they would have to multiply it by a RRA representation of 1 which brings in all the decision problem issues.

Yep, this is exactly it!

Sorry for being unclear about this. A number is being expressed as a rational times a real. In the case where the rational is exactly the number we want, we want to be able to set the real to 1, so the multiplication has no effect

Ahhh OK so it's essentially the null or identity value, saying "you don't need this component for an exact representation". That makes sense, thanks.

Because they express numbers as rational times a real, so the real in all those cases would be one. When it’s one, you do rational math as normal without involving reals.