CRA permits the use of late-filed s. 104(13.2) designations to carry back a capital loss to offset a s. 104(13.4) capital gain

In the case of a spousal, alter ego or joint partner trust, s. 104(13.4)(b) provides that income is deemed to have become payable to the individual whose death caused a deemed disposition of the trust property under s. 104(4). CRA accepts that this taxable capital gain can subsequently be eliminated essentially as described in the previous post, i.e., a late-filed s. 104(13.2) designation is available in order to carry back and apply an allowable capital loss subsequently realized by the trust - unless there is retroactive tax planning.

Neal Armstrong. Summary of 19 September 2015 STEP Roundtable, Q.6(a) under s. 104(13.2).