It appears that I didn’t put the same output filter hook on the display name in the calendar, so you can’t use the code snippet I provided here:
https://stephensherrardplugins.com/support/topic/show-full-last-name-of-volunteer/
However, the templates for the way the calendar display things can be modified to show the info almost any way that you want. Check out the docs page here:
https://stephensherrardplugins.com/docs/pta-volunteer-sign-up-sheets-calendar-display/
Scroll down to the section titled “TEMPLATES & CUSTOM CSS”
That describes where to copy the templates if you want to make changes.
Then, all you need to do is edit the sheet.php template file. Look for the section that says SIGNUP NAME LIST START. Lines 100 to 102 display the name, and currently look like this:
<span class="cal-signup-name">
<?php echo esc_html( $this->get_signup_name($signup) ); ?>
</span>
All you would need to do is change the middle line to:
<?php echo esc_html( $signup->firstname.' '.$signup->lastname ); ?>
Also, you can submit a feature request (so I can remember), and I’ll try to add that same output filter to the calendar function that gets the display name, so that the same code snippet for the main plugin will also work for the calendar display. If I have time today, I’ll try to put together a quick update to include that output filter, and any other similar filters that I may not have included in the calendar output functions.