An appeal is not a second opinion. MOM states that there will be no change in the outcome unless there is new information in the appeal, and that the appeal should be made only to address the issues raised in the rejection advisory.
Documents are not needed in every appeal. They are not required where the candidate can now meet the qualifying salary and COMPASS criteria, or where the outstanding issues have been addressed — which includes correcting inconsistencies between the qualification information in the application and the verification proof, meeting the job advertising requirements, and resolving IRAS tax matters.
MOM publishes that 85% of appeals are processed within 6 weeks. That is a published figure for appeals as a group, not a prediction about any particular appeal, and nothing here should be read as a statement that an appeal will succeed.