Yes. The new bridge will have some of the most technically advanced monitoring systems in the world. Almost all new structures on that scale would have some form of remote monitoring. The existing bridge may well have been monitored but it would have been retrospective and therefore only installed in known areas of high stress, areas of concern etc. The issues with the cables that formed the basis for the business case for a new crossing were identified using monitoring apparatus.
The bridge was never designed to carry the volume and weight of modern traffic, so it's not difficult to see why it's starting to show signs of distress.
I'm told the defects were in hard to reach areas, so it may be that these were only inspected at longer intervals, say 5-years, during detailed surveys, rather than a more general annual inspection.