That's just a standard message that has been like that for years. It used to take 6 to 12 months for the card to get manufactured and delivered.But in the letter it says"
You should received your Permanent resident card somewhere between six and twelve months.In the event that you move,be sure to advice USCIS of your changed of address referencing the above "A" number in your letter.
I was wondering why it will take 6 months to 12 months to get the card.