using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var text = "aa12,af43,ad46";
    	var pattern = @"^(?:([a-zA-Z]{2}\d{2})(?:,\b|$))+$";
    	var result = Regex.Matches(text, pattern)
    		.Cast<Match>()
    		.Select(x => x.Groups[1].Captures.Cast<Capture>().Select(m => m.Value))
    		.ToList();
        foreach (var list in result)
        	Console.WriteLine(string.Join("; ", list));
	}
}

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