Versions /Planned Independent Requirement

Guys,

In MD63 when I look for requirement it' showing me two active requirements.One is 01 and another one is X9.  I can see in under "Define Versions Numbers" both are defined .My questions is why 2 active requirements are coming and where is the assignment is happening between versions and PIR? How I can disable X9 and will it have any impact on system ?

Thanks