Yeah, chiming in with a bit of additional explanation: AO3 won't let you put "Natalie Lambert" by itself into the "Relationships" field; it'll give you an error, because AO3 has that specific tag already as a character. (And if it does let you, this will cause problems for everyone else using that tag, forever.) The "Solo: Natalie Lambert" language is solely to allow the exchange to get around that. Exchanges may do something similar with "Group: Natalie/Nick" in the "Character" field for similar reasons.