using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<A> first = new List<A>() { new A("FOO", 1), new A("BAR", 2) };

        List<B> second = new List<B>() { new B("FOO", 6), new B("BAR", 3) };

        List<C> third = new List<C>() { new C("BAZ", 5) };

​

        var allStates = first.Select(a => a.Status)

            .Concat(second.Select(b => b.Status))

            .Concat(third.Select(c => c.Status))

            .Distinct();

        var result = allStates

            .Select(Status => new 

                    {

                        Status,

                        ValueA = first.FirstOrDefault(a => a.Status == Status),

                        ValueB = second.FirstOrDefault(b => b.Status == Status),

                        ValueC = third.FirstOrDefault(c => c.Status == Status),

                    });

        foreach (var item in result)

        {

            Console.WriteLine(item);

        }

    }

}

​

public record A(string Status, int ValueA);

public record B(string Status, int ValueB);

public record C(string Status, int ValueC);

​