Also, I don't think I need to worry about being on the wing's red list for 2018, as my application for COS is listed as Alternate, which means I have wing approval.
Under eServices > Activities Application > Activity Status:All approved applications are listed as "Alternate" until the initial slotting takes place in March.A status of "Awaiting Wing Approval" means your application is complete, approved by your unit commander and is being reviewed by your wing commander.A status of "Awaiting Unit Approval" means your application is complete and is being reviewed by your unit commander.Is Wing approval part of the initial slotting in March, which would be something different from the Wing approval that is required for approved applications to be listed as Alternate?
Each wing likely handles the process a bit differently. Some hold review boards to determine while others may simply mass-approve and probably many other methods as well. Once your Wing commander (or delegate) approves, the activity itself still has to actually slot an applicant into the activity - that's what will take place in March. Overall:Application>Unit Approval>Wing Approval>Activity Slotting.
Back to the original question.IACE does their slotting manually, so the rankings won't have an effect on COS or IACE. If you are slotted for IACE, your preference for COS will be removed, because they have overlapping dates. Same would apply for IACE, however, IACE keeps their original list and moves people up when an opening occurs. If you are selected for one, but can't go, decline as early as possible and restate your other preference in e-Services. That way you can get on the alternates' list again. For IACE the way you answer the questionnaire is important. It's not just do you have experience, but can you explain your experience. Can you actually answer that they are asking, rather than providing just an answer to something close to the question. Did you completely answer the question? It's best to review all of the questions in each section before answering. Some people will copy/paste their answers for multiple questions; that's not answering the stated question. They are similar, but very specific in their differences. Since you declined in early April last year, there shouldn't be any issue with getting slotted again. For practical purposes, that is declining immediately. It's the guys that wait until a couple of weeks out that the staff gets heartburn over. There's an old sayin' "I've got good news and bad news for you. The good news is that someone at NHQ knows you. The bad news is that someone at NHQ KNOWS you." Be polite in your correspondence with NHQ and activity staff, keep them up to date on possible issues and you shouldn't ever have to worry. Good luck!