[XML-Entities] Question regarding some Unicode sequences

Hello,

I noticed that the Unicode sequences of more than one codepoints are
assigned to some entities which already had single Unicode codepoints
representation at the time of addition to MathML; e.g. "race" entity from
isoamsb set is mentioned as U+223D U+0331 (REVERSED TILDE, COMBINING MACRON
BELOW) while it can also be presented as U+22CD. Is there any specific
reason for this preference?

Thanks.

Shervin
↪ shervinafshar.name <http://www.shervinafshar.name>