My experience suggests that there is no link between YL and IL. Majority of the folks received IL within 6 weeks of giving FP. Few received it after 2 to 3 months gap and mine, after 4 months gap. One thing I can tell for sure is, IL depends on how fast NBC center receives FBI feedback and how quickly they can retrieve your A# file. They need these two before they transfer your case to local DO. In my case, A# file is the problem and they waited for 4 months to issue IL, that too after contacting local Senator's office. Offcourse, my A# file is still missing even after the interview.