Working the examination: Differences between Ss 14, 15 and 16

These are:

Ss14/15 refers to the person(s) by whom the claim is made, while S16 refers to the person(s) to whom a tax credit has been awarded. Although this difference in wording does not affect your general approach to working the examination, it is important to identify in each case which type you are examining so that you issue the appropriate information notice (cross-reference CCM5130 for S14 and S16, and CCM5150 for S15 Information Notices).
An important difference is the requirement at S16(2) for you to believe that the tax credit has been awarded at the wrong rate (S16(2)(a)), or that the claimant(s) have ceased to be, or never were, entitled to tax credit (S16(2)(b)). CCM4190 explains why you will always have good reasons for examining claims post-award
Ss14 and 15 are not tied to the year for which the claim is made. So if a claim is made in advance of the year, or a claim or change of circumstance is made retrospectively, you can ask questions of the claimant(s) or third parties at any time before making a decision on the claim or CoC. The use of S16, however, is limited to the year for which the award is made. S16 only applies during the period for which the award is made, i.e. from 6th April - 5th April, so again, the S16 powers cease at 5th April.

Claimant Compliance Manual