@chococrinkle you can only claim work experience for the last 10 years, that's the maximum. I'm currently handling a case, regional sponsorship as well. We supplied ITR Lang for all employment years we're claiming, granted yung SA sponsorship under 2 weeks. We submit all docs except payslips sa DIBP. It just depends on the case officer kasi e. DIBP just got back to us and requesting for further pay evidence. So in the end, you can try with everything that you have now and the case officer will just get back to you if they want more docs.
With regards to your timeline, I think it'll be too tight. If you say you'll get the renewal assessment by 2nd week of December at the latest, you still need to apply for SA sponsorship which takes another 2 weeks. Considering that it's Christmas period and all, I don't think you'll here from SA until early next year.