Currently when producing products which require a lot the number must be explicitly set. But most of the time the lot number can be autogenerated using a sequence as the proupose of this field is to link the products with the production, so all the components and operations can be easly found.
This is specially usefull when working with serial numbers.
I think we should allow to set a lot sequence on production configuration and use this sequence to automatically create a lot for each output product that requires a lot if not set
As this may not be usefull for all tryton setups probably this should be part of a new module.