
I prefer to have the waiting lists in place, as I like to have established a relationship with the potential owners, and know that their decision to have a puppy is not a rash one, but as you find expect people to drop out.
In fact if I know another breeder has a puppy left or cancellation I will ofte4n contact people on my list suggesting they may want one sooner (bird in the hand), as I feel what goes around comes around, and I'd rather have a new breed convert and a puppy on the ground homed sooner.
I update people as you say at various stages and add to my email that if they do not respond to say they are still 'on board' then I assume they have changed their minds.
By the time a pregnancy is confirmed I rarely have people drop out, but up until then I expect to loose more than half depending on how long they have been on my list.
On the other hand as others have said some people faithfully stay on the list for ages, even over a year.
Also as my breed is numerically small the number of good puppy enquiries are unlikely to al amterialise in a short space of time (say 6 weeks once pups a re on the ground), it's often feast or famine in our breed, no pups to be had, and then two or three litters born, and fi an imbalance of sexes then there will be pups taking longer to find the right homes.
I always warn any new breeder to expect to allow three months tot have all of a litter homed, and would consider having all pups go at 8 weeks unusual, even if all booked.