They take a lot of inspiration from the American Revolution. Robert Townsend posed as a loyalist newspaper writer and got chummy with a ton of British soldiers who would get drunk and give him all kinds of intel, he would then write it down on paper, put the paper in a box and bury it in the wood so that another patriot would dig it up and give it to a local lady who would rearrange her hung laundry in code for the patriots to look at. I imagine stuff like that is happening here too.