C# – Conditionally initializing a string list

I am writing a program that needs to be able to process data from a number of different sources. The sources output data in a variety of formats. So, depending on which source is being used, I need to initialize a string list with a different set of column headers. The quantity of headers varies between 10 and 18 columns depending on the data source.

Essentially, I need a clean method to conditionally initialize a list. I have three working solutions but I am not sure which is the cleanest/best practice:

• Example #1 requires that I add each header to the list line-by-line. With the number of potential sources and columns that need to be added for each, this list gets pretty long.
• Example #2 requires that I use {} around each case statement to limit the scope so that I can declare the dataHeaders list individually in each case statement. I have never encountered a situation wherein I had to limit the scope to an individual case statement and as such, I suspect it is bad practice.
• Example #3 seems like the best option. I actually implemented this one as I was writing this question. I don't really see any drawbacks here but I thought I'd still pose the question anyhow.

Is there a better/cleaner way to do this? If not, which example is the best practice?

Example #1:

List<string> headers = new List<string>();
switch (dataSource)
{
    case "Source 1":
        headers.Add("header1");
        headers.Add("header2");
        headers.Add("header3");
        headers.Add("...");
        headers.Add("header18");
        break;
    case "Source 2":
        headers.Add("headerA");
        headers.Add("headerB");
        headers.Add("headerC");
        headers.Add("...");
        headers.Add("headerJ");
        break;
    default:
        // TODO: Handle bad sources.
        break;
}

Example #2:

List<string> headers = new List<string>();
switch (dataSource)
{
    case "Source 1":
        {
            List<string> dataHeaders = new List<string>() { "header1", "header2", "header3", "...", "header18" }
            headers = dataHeaders;
            break;
        }
    case "Source 2":
        {
            List<string> dataHeaders = new List<string>() { "headerA", "headerB", "headerC", "...", "headerJ" }
            headers = dataHeaders;
            break;
        }
    default:
        {
            // TODO: Handle bad sources.
            break;
        }
}

Example #3:

List<string> headers = new List<string>();
switch (dataSource)
{
    case "Source 1":
        headers.AddRange(new List<string>() { "header1", "header2", "header3", "...", "header18" })
        break;
    case "Source 2":
        headers.AddRange(new List<string>() { "headerA", "headerB", "headerC", "...", "headerJ" })
        break;
    default:
        // TODO: Handle bad sources.
        break;
}