I-551 Registration Number same as Alien Reg #?

Is the Registration number on the I-551 stamp in the passport the same as the Alien Registration Number? The Registration No. on the I-551 stamp has 8 numbers. I know Alien # starts with an A and the rest with 9 numbers, but the I-551 stamp has only 8 numbers. We are still waiting for the green card of my dad whom I'd like to apply for Medi-cal right away. They need the Alien Reg. #. Thank you for anyone who can help!

Someone asked a similar question on yahoo answers:

Does the I-551 stamp on the passport contain the Alien registration no.? Just add A before the registration N? - Yahoo! Answers

Open Question Does the I-551 stamp on the passport contain the Alien registration no.? Just add A before the registration N? There's a registration no. on the I-551 stamped passport, is that the alien registration no? Just add A before the nos?

When you apply for your GC, you would have received the Receipt Notice from USCIS, within that form, you can view the Alien Reg # Starting with A --- --- --- followed by numbers.
Hope this helps.

Thanks,
Bhaspro

Thanks!!