xabbo-scripts/Scripts/FindHiddenHeader.csx

var outProperties = Out.GetType().GetProperties();
var unknownPacketIds = new List<short>();
for (short i = 0; i <= 4000; i++) {
    try {
        Header header = null;
        if (Messages.TryGetHeaderByValue(Destination.Server, Client, i, out header)) {
            string headerName = null;
            foreach (var prop in outProperties) {
                try {
                    if (prop.PropertyType.Name.Contains("Header")) {
                        var outHeader = prop.GetValue(Out);
                        if (outHeader != null) {
                            var flashProp = outHeader.GetType().GetProperty("Flash");
                            if (flashProp != null) {
                                var flash = flashProp.GetValue(outHeader);
                                if (flash != null) {
                                    var valueProp = flash.GetType().GetProperty("Value");
                                    if (valueProp != null) {
                                        var value = valueProp.GetValue(flash);
                                        if (value != null && value.ToString() == i.ToString()) {
                                            headerName = prop.Name;
                                            break;
                                        }
                                    }
                                }
                            }
                        }
                    }
                } catch { }
            }
            if (headerName == null) unknownPacketIds.Add(i);
        }
    } catch { }
}
foreach (var id in unknownPacketIds) {
    Log($"Unknown packet ID: {id}");
}