`alphanumeric` style: How to get disambiguation letters (e.g., [ASS96a] and [ASS96b]) in bibliography labels?

OP of the referenced forum post here:

and it should be noted that, depending on what one is looking for, only partial solutions currently exist for year disambiguation. In particular, the only approach that ensures bibliography entries have year disambiguation also breaks the formatting, in that the line wrapping in the bibliography proceeds to have new lines flushed left with the labels (e.g. [ASS96b]), rather than having the entries treated separately.