I'm not competent to answer that, but the "merged glyph" versions of the other four modern era names date from older encodings like EUC and shift-JIS, and are p

I'm not competent to answer that, but the "merged glyph" versions of the other four modern era names date from older encodings like EUC and shift-JIS, and are presumably in unicode for compatibility. So the rationale for adding a new one may just be extending that set.