It can be a good idea to provide supporting documents with your letter of explanation that help back it up. For instance, if your letter is about a gap in employment, you could include a termination document from your old employer to establish you were laid off (and not fired for cause). If you have since returned to the workforce, including recent pay stubs or other proof of the new job and its pay can be helpful. Similarly, if your letter of explanation is about a past credit issue, it’d be a good idea to include a recent copy of your credit report that shows your improved credit score.