Section 257EA | Time for making claims for SEIS relief
From legislation.gov.uk
(1)A claim for SEIS relief in respect of shares issued by a company in any tax year may not be made later than the fifth anniversary of the normal self-assessment filing date for the tax year.
(2)If section 257AB(1) and (2) applies in the case of any issue of shares as if part of the issue had been issued in a previous tax year, this section has effect as if that part and the remainder were separate issues of shares (and that part had been issued on a day in the previous tax year).