Variable Data Addressing

I am working on an old project design by somebody else. I am trying to upgrade the PLC from Micro to Momentum. He implemented a master/slave communication. When looking at how the data is mapped from the slave to master. I see that he uses the same variable name but different address. He was using the BIT_TO_WORD block on the slave side and WORD_TO_BIT on the master side. Software I am using is Concept 2.6.

Please could anyone why he uses the different rather than the same address on both the master & slave?