Just to muddy the waters here.... consider the 300 series as having the most designations of all:

300b(?), 300c, 300d, 300D, 300E, 300CD, 300CE, 300TD, 300TE, 300SD, 300SE, 300SL, 300SDL, 300SEL..... have i left any out?

The little letters never make it to name plates. On your 220Sb its pronounced "Sb" not sb. Think on it as 2nd run of the incomparable 220S that began in round body form.