Mac address problem

I found below delphi code for get mac address.I test this address with my alot of users.I have seen that Some users have same mac address? is it posible? Or is this code wrong?
How can I get unique mac address?

function GetAdapterInfo(Lana: Char): String;
var
  Adapter: TAdapterStatus;
  NCB: TNCB;
begin
try
  FillChar(NCB, SizeOf(NCB), 0);
  NCB.ncb_command := Char(NCBRESET);
  NCB.ncb_lana_num := Lana;
  if Netbios(@NCB) <> Char(NRC_GOODRET) then
  begin
    Result := '';//'mac not found';
    Exit;
  end;

  FillChar(NCB, SizeOf(NCB), 0);
  NCB.ncb_command := Char(NCBASTAT);
  NCB.ncb_lana_num := Lana;
  NCB.ncb_callname := '*';

  FillChar(Adapter, SizeOf(Adapter), 0);
  NCB.ncb_buffer := @Adapter;
  NCB.ncb_length := SizeOf(Adapter);
  if Netbios(@NCB) <> Char(NRC_GOODRET) then
  begin
    Result := ''; //'mac not found';
    Exit;
  end;
  Result :=
    IntToHex(Byte(Adapter.adapter_address[0]), 2) + '-' +
    IntToHex(Byte(Adapter.adapter_address[1]), 2) + '-' +
    IntToHex(Byte(Adapter.adapter_address[2]), 2) + '-' +
    IntToHex(Byte(Adapter.adapter_address[3]), 2) + '-' +
    IntToHex(Byte(Adapter.adapter_address[4]), 2) + '-' +
    IntToHex(Byte(Adapter.adapter_address[5]), 2);
except
  result := '';
end;
end;

function GetMACAddress: string;
var
  AdapterList: TLanaEnum;
  NCB: TNCB;
begin
try
  FillChar(NCB, SizeOf(NCB), 0);
  NCB.ncb_command := Char(NCBENUM);
  NCB.ncb_buffer := @AdapterList;
  NCB.ncb_length := SizeOf(AdapterList);
  Netbios(@NCB);
  result := '';
  if Byte(AdapterList.length) > 0 then
    Result := result + GetAdapterInfo(AdapterList.lana[0])
  else
    Result := ''; //'mac not found';
except
  result := '';
end;
end;