I took Accutane many years ago. I was also told that if I ever wanted to have a baby, I would need to stop taking Accutane for at least 2 years.
What your doctor is most likely using is the information given for someone who is taking Accutane for a short time period. If one is taking Accutane only to treat acne, it's only taken for about three months. For such a short term, one month is a somewhat reasonable waiting period before conceiving.
However, it is harder to find information about what the waiting period should be if you have been taking Accutane long term, at least on the internet.
I would suggest calling F.I.R.S.T. or writing to them. Their web address is www.scalyskin.org
I bet someone in the office knows what the waiting period should be, or can give you the email address of one of the dermatology physicians/researches affilated with F.I.R.S.T. If you are a F.I.R.S.T. member and recieve their newsletter, send a letter in and I bet it would be answered in the newsletter.