There are lot of root causes involve in failure or unsatisfactory cube test results.
It is not easy to detect the problem either with casting, curing, testing, production, materials etc.
If you are sure about, your concrete is failed, then whatever you are doing further is just in the interest of hiding the blunders which could popup in the future.
If that is not the case, you are on your journey to find the actual root cause to fix the issue.
If I get a free time, will definitely write a book on this subject as this is a very vast and involves multiple aspects and its just like creating a movie which has all genres packed in it to highest level. there are scene which are full of comedy, you find some crime scene, suspense, thrill.
In short, it takes lot of examination to conclude the problem and taking decision.
We should always cast higher number of cube sets or atleast cube sets as per IS code frequency this gives us ability to test the concrete in further ages to check the strength gain curve and also for understanding problem in particular lot of concrete or cube casting activity.
If you had extra sets of concrete cubes, you saved a lot for your company because it cost less than what you are going to spend and time is always money which you do not allow to loose due to extra sets.