Those sound about right. So for most active investors that means directly owning only A and better stuff and holding a lot of lower quality stuff via junk bond funds if one's up for some risk. With tax rates so low nowadays, there's not much case for many people to have munis, other than for diversification. They do have a strong track record going back to the Great Depression and long before that.
Most people should stick with short maturities but that's mostly about inflation risk. I'll go out about 10-15 years but laddered with shorter stuff such as MM funds and bank CDs.
I've only ever had one bond default, a muni revenue bond, but it was insured.
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