I can't believe Deb says 20-30% of bags are lost to dunking, unless she is dunking newer, lined bags. I've never lost a bag to dunking and I've only known of a few that have been lost on the forum. And it depends on how to define lost. Some people have ruined bags by dunking because there was a large amount of ink that spread to the exterior. They aren't exactly lost, just not necessarily improved. The only truly lost bags were those that were a lost cause already - the leather had rotted so much that putting them in water caused them to disintegrate. I've only heard of that once or twice. I've seen a few bags listed for sale that look like they would disintegrate too, but it's pretty obvious.
If you only dunk unlined vintage classic bags, you shouldn't have a problem. These bags are almost always improved by dunking, as long as you do it correctly and use plenty of conditioner promptly. You can also dunk some lined bags, like Sonomas, with success.
You are never going to find 100% agreement on the Internet.