Hi Sarah, its from mumbai consulate in india, I received p4 packet 2 days before interview date, and they just send you approved copy of 129f, everything is well explained on the consulate website,,
I did not wait for the welcome letter from embassey, only max mohali and max mumbai ask for it to set up a medical appointment, so I scheduled at max Delhi and they did not ask for any welcome letter just FTP letter copy and appointment letter copy, I had scheduled interview myself after I recevied FTP letter. although I also received welcome letter 3 days before interview but no one asked for it at interview, I hope that helps, good luck to you,,