welcome = approval
We received welcome notices - all three in the family me (primary), spouse and child after the approval and stamping in Baltimore (interview case), and after receiving the physical cards, and that too, 2 copies each.
The timing of the welcome notice was funny, b'cos it says your card has been ordered and will receive in .... blah blah ....
And the cards had arrived a week ago.
I think a welcome notice is nothing but an approval notice.
Maybe those who were approved (I-140) for CP get it ! My I-140 was approved for CP, but I went for AOS.