I thought of posting my experience here:
"Guys, quick advice:
Just called FBI, and the fingerprints that I submitted on october 1st are rejected, so take precautions and send 3,4,5 sets of fingerprints because you dont want to hear that you need to submit again in 14 weeks :S:S, for people sending today that is until may :S:S...
... luckily I sent additional fingerprints sets on Oct 6th and those were fine and report mailed this morning 8) "
By the way, my fingerprints were done at a US Police Station, so even that were taken by an expert, does not guarantee acceptance...
at least the strategy of sending a request with multiple fingerprints and then after a week submitting a separate request with multiple fingerprints seems the most suitable one to minimize the risk of rejection and begin the process from zero after 15 weeks of initial submission
Hope my experience helps other people on the same journey!