All cards examples have the same structure regarding the content:
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">This is a wider card with supporting text below as a natural lead-in to additional content. This content is a little bit longer.</p>
<p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
</div>The one in Image overlays doesn't contain the <small class="text-muted">...</small>.
Since .text-muted makes it non-accessible, I chose to only add the <small> HTML element.