I agree that the ticket allocation seems to be random. I am a member, booked my tickets for this year on return from last years race. I wanted camping passes for Tetre Rouge, but was allocated Bleu Nord. A friend of mine didn't order until August and got his allocation, no problem.
Having said that, it's still woprth being a member for the discount and the roadside assistance, which I have made use of when the started on the Black Granny expired in the heat on returning a couple of years back.
PS Have already ordered next years tickets.