Anyone using gold detecting guides/maps & expecting to be put directly onto a patch of gold will be very disappointed! The only usefulness these things have ever had is showing where gold was & might still be if your lucky. These maps/guides are best used to get you onto known gold areas - as my old mate Meta once said when you get there put them back in the glovebox. Look for harder to get to or less obvious areas within/around them.
As for flogged areas my interpretation of a flogged area is one that's seen a lot of activity which can lessen your chances. Nobody is that good that they get it all - some like to think they are or do. Unfortunately modern day junk has a habit of reappearing or being replenished by pigs. Some of the pigs also like to leave open holes, throw junk away again after they dig it or even put it back in the hole & bury it again.
If I'm in a "flogged" area modern junk i.e. 22's, bird shot, cans etc. doesn't excite me or make me think it hasn't been detected well. Finding old junk can though.
Another thing is that junk piles continue to disintegrate & spread over a wide area. Even something as simple as a small metal container/drum can spread in a wide radius or even right down a gully. Most detectorists generally avoid these places especially with PI's.
A lot of these "flogged" areas are huge & even though some ground may have been detected numerous times gold still gets missed & there is also other ground that may have had very little attention for a variety of reasons like not being an obvious looking gold area, hard to get to, covered in branches, overgrown & so on.
I've flogged a few little patches with the SDC - sometimes going back 5-6 times & found gold I'd missed. Different day, different approach, different weather, less junk targets now etc. etc. etc. My last trip to a nearby spot that I'd "flogged" with the SDC produced 3 little nuggets & 3 birdshot for about 2hrs. When I first detected it I was getting maybe 50 to 100 junk targets to maybe 6 little nuggets. I've got no doubt someone else would find gold there as there was areas with very high amounts of metal fragments that I just left alone after numerous junk targets & no gold I concentrated on where I was getting gold in amongst the trash. I reckon a lot of areas would be similar for similar reasons?