The board has been compromised due to the paper face being torn off unfortunately. The paper serves a couple of purposes, it has thousands of microscopic pores in it to help plaster adhere to it but it also helps to control the suction/absortion of the water in the plaster or in this case the adhesive. If you attempted to plaster that the remaining brown paper would start to bubble up and delaminate from the core. I suspect it would do the same with the tile adhesive as a result of the water content of the adhesive as it will remain wet for a number of hours. I suppose priming them and then tanking might help, but why bother, just replace them.