The exact words from the patch notes are:
Reduced the number of maximum of stacks of Retaliation allowed to five (was 25). Duration still stacks.
Retaliation to my knowledge stacked in duration unlike Might say which stacked in intensity. This note therefore makes no sense when it refers to stacks of Retaliation.
Unless it means you can only extend the boon duration 5 times but it’s rather unclear.