using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var skills = new List<Skill>(){

            new Skill() { id=1, year = 9, xp = 95 } ,

            new Skill() { id=2, year = 5 } ,

        };

        int maxYear = 10, maxXp = 100;

        List<string> resultList = skills

            .Where(skill => skill.year <= maxYear && skill.xp <= maxXp) // skip invalid

            .SelectMany(skill => Enumerable.Range(skill.year, maxYear - skill.year + 1)

                .SelectMany(y => Enumerable.Range(skill.xp, skill.xp == 0 ? 1 : maxXp - skill.xp + 1)

                    .Select(xp => xp == 0 ? $"{skill.id}-{y}" : $"{skill.id}-{y}-{xp}")))

            .ToList();

​

        Console.Write(string.Join(Environment.NewLine, resultList));

    }

}

​

​

public class Skill

{

    public int id { get; set; }

    public int year { get; set; }

    public int xp { get; set; }

}