R. v. CD, 2021 NUCA 21, November 25, 2021, at paragraphs 13 and 14:

…trial judges have an inherent ability to edit oral reasons, for example, by correcting the grammar or method of expression or by adding citations: PricewaterhouseCoopers Inc v Perpetual Energy Inc., 2021 ABCA 16 at para. 61. On the other hand, an express reservation of the right to edit or supplement does not enlarge the scope or nature of enhancements of reasons that are permissible.

The issue of “supplemental reasons” can arise in different contexts:

(a)  A trial judge may simply declare an outcome with “reasons to follow”: e.g. R. v Teskey, 2007 SCC 25, [2007] 2 SCR 267 (verdict); R. v Sundman, 2021 BCCA 53 at paras. 55-56 (mid-trial rulings);

(b) The trial judge may have lengthy reasons prepared, and essentially finalized, but due to the length read only a summary, followed by immediate release of the longer version: e.g. R. v Vander Leeuw, 2021 ABCA 61 at para. 9.  

(c) The trial judge may announce his or her decision, but then correct that decision when an obvious error or illegality is identified: e.g. R. v Vader, 2019 ABCA 191 at paras. 56-57, 89 Alta LR (6th) 146.

(d) The trial judge gives reasons that appear to deal with all the issues, and outline all of his or her reasons, but then releases truly “supplemental” reasons that add arguments or issues: e.g. Perpetual Energy at para. 61.

The scope of permissible variations between the original oral reasons and the supplemental reasons varies with the context. In general terms, a trial judge may edit oral reasons for punctuation, grammatical errors, citations and the like, but may not revise, correct, or reconsider the words actually spoken or make changes of substance: R. v Wang, 2010 ONCA 435 at para. 9, 256 CCC (3d) 225; R. v Desmond, 2020 NSCA 1 at paras. 24-25, 384 CCC (3d) 461.