The realistic answer here would be that during Spider-Man 75, there was most likely a Miles Warren clone or even the real Miles Warren down in the street watching Peter and Norman fight. He saw Ben's sacrifice and probably ran over and Ben and told the crowd something like "no worries. I am a doctor." He probably quickly took a sample of Ben's DNA and ran off. Ben is dying so he can't tell someone jacked his DNA. Peter comes down and Ben dies. Then Ben is brought back by Jackal. There is zero way jackal was hanging around watching peter spread ashes because technically we never saw that epilogue unless we bought the TPB or the recent clone epics. The crowd around ben is the best answer for how Warren could have been able to clone him any point after his death