I have fitted loads of stone and tiles with this method, you didnt even really need the sbr bond in the slurry in this circumstance the supplier gave this advice as overkill ,the slurry needs to be creamy inconsistency if its too wet it doesnt give a good bond to the sand and cement also the sand and cement bed must bed semi dry like floor screed if its too wet or too dry you can get problems, the only other issue is the compaction of the bed under the stone, sometimes when fitting, you can hit one side down too far then tap the opposite side to bring the tile level causing the tile to see saw on the bed this will cause the tile to come loose as only a small part of the underside of the tile is in contact with the bed and a void is formed, when fitting work this method we tap the work with a hard wood stick to see if they were fully bonded any voids were flood grouted the following day which makes the floor completely solid, this method is by far the best method for this job, as Dave says now every thing is dry just take the loose ones out and restick with adhesive grout them with flexible grout and the job will by fine