I'm pretty sure it's a legacy system. Once it's in place, it stays there because it's useful to be able to compare different issues of bonds with earlier issues from the same issuer, for example.
I suspect that the reason they don't have ratings with a numerical score is that when they started, there wasn't any sort of clear numerical relationship between the ratings and risk, and they didn't want to imply any.
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Date: 2010-01-15 05:41 pm (UTC)I suspect that the reason they don't have ratings with a numerical score is that when they started, there wasn't any sort of clear numerical relationship between the ratings and risk, and they didn't want to imply any.