I keep seeing people concerned about decommissioning their fleet carriers 'Before' 6 days... But from what's been said so far, there is no reason to decommission before the split If you are active on 4.0.... You're saying 'again' so I'm guessing you already did the profile transfer / crossgrade. The issue with carriers is when the split happens, the people who decide to move forward with 4.0 will have to decide if they want to maintain the carrier in 2 different unconnected universes, or to decommission the old carrier so the upkeep doesn't bleed the cmdr dry. This is not a transfer issue like before. At the split I will decommission my old carrier to stop the upkeep and give my old cmdr the money in case I ever go back to 3.8.
Edit... you also said "I thought I was good. Turns out I wasn't. Now".... Are you saying that because you actually had a problem before today or because everyone keep saying not enough time to decommission carriers..... Only the people who haven't successfully done the profile transfer from 2 months ago should be concerned... Are you playing on 4.0 horizons or odyssey? if so you're good to go. You can do whatever with your old carrier whenever you decide to (after the split). People have been requesting that cmdrs move their old unused carriers to empty systems though to minimize clutter.
Personally i'll just continue in live and let the legacy account stagnate. The FC will sell itself eventually anyway.