Mike. I know Fleetwood. My lad fished from there when he first started work.
He was on the old Glen Rushen. Still works on the fishing for Vic Buschini out of Shetland.
To answer your question, When I was trad it was common practice to do them twice. The glass is not the real problem, it's the frames. You touch a frame when your detailing with your scrim, and it's contaminated. Detail the next pane and you will leave a streak. It can save you time in the long run if you wizz round the frame with your cill cloth before you start cleaning the pane.
When I was just using an applicator and blade, I used to put loads of water on the glass. This helped, but when I bought my first back flip it made the job a lot easier. Using it as a single pass tool, I could do the pane twice without lifting it off the glass. The Wagtail combo was even better, with this dog eared, and being very careful, I didn't have to detail at all.
WFP makes the job a doddle providing you pay enough attention to the frames. I know that some guys, Ross in particular, are still having problems. Any runs, must come from the frames though, It can't come from anywhere else. I'm lucky in so far as 95% of my windows are plastic. Scrub the frames thoroughly and I have no problems. If the frames are wooden, or have any crevices where salt can lodge, it can be a different matter. Hope this helps Dai