I believe the majority of the time this will be clear. In any cases where it isn't 100% clear (not all starters rested), I will try to resolve the following ways (with my best judgement):

If the best healthy players on a team play and other lesser players or ones with preexisting minor injuries are rested I will not consider that resting the starters.

If starters start the game and then are pulled midway through the game to rest them I will not consider that resting the starters as they played.

Please feel free to ask any clarifying questions and I will answer the best I can.