How to correctly express a successful job (where others failed) in a cover letter [closed]

Solution 1:

You can say you "Completed" the job, or that you "saw it through to the end", and that you "excelled at' the job to emphasize your aptitude in completing it.

If you want to emphasize that you are the one who completed it, and that neither of the other individuals could, you could say you "made it work", which tells your prospective employer that it was a job that had previously not been working, and that you "made it work and improved the quality of the product" both states that you finished it AND improved the job.

I don't think there's any one word to describe what you've done though. You may be better off just explaining the exact situation as such: "Where two previous employees failed to complete [this job], I was brought on and finished the job, meeting and exceeding the standards."