Trouble Appending Dropdown Values

Hello,

Trying to update the Lead Source Dropdown with a few additional options.

I would think the two following classes would work, but I do not get any UI changes. I think I am missing something simple.

    public class CRLead_Existing : PXCacheExtension<PX.Objects.CR.CRLead>
    {
        public static bool IsActive() => (true);

        #region Source        
        [PXRemoveBaseAttribute(typeof(CRMSourcesAttribute))]
        [PXMergeAttributes(Method = MergeMethod.Append)]
        [PXDBString(1, IsFixed = true)]
        [GPLeadSource]
        public string Source { get; set; }
        #endregion

    }

 public class GPLeadSourceAttribute : CRMSourcesAttribute
    {
        public const string Email = "E";

        public const string Text = "T";

        public GPLeadSourceAttribute()
        {
            Array.Resize(ref _AllowedValues, _AllowedValues.Length +2);
            _AllowedValues[_AllowedValues.Length - 2] = Email;
            _AllowedValues[_AllowedValues.Length - 1] = Text;
            Array.Resize(ref _AllowedLabels, _AllowedLabels.Length + 2);
            _AllowedLabels[_AllowedLabels.Length - 2] = "Email";
            _AllowedLabels[_AllowedLabels.Length - 1] = "Text";
        }

    }