LMiller7 said:
SMART provides a valuable warning but you should never rely on it. You should make backups when everything is working well and not wait until you receive a warning. The time between receiving the warning and drive failure may be too short or one of many things may happen that SMART has no knowledge of. The drive electronics is just one of many. Electronic devices typically fail without warning or apparent cause.

Many warnings outside of computers work the same way. The "Check Engine" light in a car provides a useful warning that something may be wrong and action needs to be take. But the lack of the warning doesn't mean all is well.
Is Dell S.M.A.R.T. smarter? The reason I ask this. When I had the motherboard replaced under warranty, After replacing the motherboard he ran the bios system testing. The hard drive test include two S.M.A.R.T. type test plus some other type of test. It came back with no error messages.