The instructions for Form 5498 are a bit ambiguous, but payers interpret the instructions to mean that contributions are reportable on Form 5498 of the year for which the contribution is made, box 1 for regular traditional IRA contributions and box 10 for Roth IRA contributions.

If you made a contribution for 2015 and it does not appear on your 2015 Form 5498, it suggests that the custodian has recorded it as a current-year contribution rather than as the previous-year contribution.  Some custodians issue Forms 5498 early in the year and issue a corrected Form 5498 to add a contribution made for the previous year if one is made.