Uni-assist is a centralized service for evaluating international students' applications in Germany. If universities have different application deadlines, you can submit your documents to uni-assist once, and they will keep them on file. You can then select which universities you want to send your documents to and specify the respective application deadlines. You won't need to submit your documents again, but you might need to pay an additional fee for each university choice. Check uni-assist's website for the most up-to-date information and specific instructions.