Please be informed Altera does not provide die marking verification.
Altera does not provide support for devices purchased via the gray market and this includes part marking verification. Devices purchased via the gray market do not meet Altera's commitment of high quality devices because there is no quality control in the gray market.
If the devices were purchased via an authorized distributor, you should have no doubts that the devices are authentic Altera® devices.
You should only purchase Altera products from authorized distributors. For a list of authorized distributors, you can refer to http://www.altera.com/corporate/contact/con-index.html