I am inclined to agree about the lack of problem from old concrete tiles that have lost their glaze. Now that you have replaced the tiles that were actually cracked, can you monitor to check for any continued leaks? If there are no leaks you have fixed the problem for the cost of a few spare tiles.
Among our townhouses, all the tiles are weathered concrete from the 1970s. One unit had a recoating treatment done (in the ACT unit owners in townhouses (class B units) are responsible for maintenance of the unit) and it does not look good having one unit with a shiny new surface.