System Lookup Value "Legal Name"

The system lookup value "Legal Name" in Admin > Lookups > Additional Name Types is tied to the Legal Name feature described on the Applicant Name Block page.

That system value does not appear in the Type dropdown when adding additional names in the conflict search block:

As shown, you can add a non-system value to the lookup list. It can even be called "Legal Name".

But check out the feature mentioned above for a fuller experience.