If it is like earlier Tesla models, then yes, they will make many Founders' cars first, then start sig production.
On the plus side for sigs, the Founders' group can provide direct feedback internally to fix any last minute problems before the sigs get their cars.
I think this has been the plan all along... After they start making sigs, there is a chance they will still pop out some more Founders' cars if they see the need.
I am not sure what it takes to get on the Founders' list, but I suspect it involves having a substantial investment in TSLA.