Re: Bottom paint flag coat theory vs. reality
Personally, I think that you can tell whether it needs to be redone without a flag coat. The first year or two after you strip the bottom you might see a bit of the barrier coat at the next haulout but after that, most people will have enough paint buildup that they would never see a flag coat again unless done yearly.
We essentially have a flag coat as the PO switched bottom colors for asthetic reasons. We see a little bit of it every season but it doesn't change our painting habits.