I've never skipped a rank, however, I went from Nidan to Sandan in one year. Reason, I'd been a JBB for just over 5 years, and during that time, my Dai-Soke trained me to Sandan level. So, when I turned 18, I tested for my Shodan, then a year later I tested for my Nidan and because I was more than ready my Sandan, per my Dai-Soke, I tested for my Sandan one year after my Nidan instead of waiting the tenure of 2 years minimum. After that, tenure had to be achieved per our Soke.