When grouping by date tag make sure you add the date tag somewhere in the content even if it's in a HTML comment so EE knows to render the tags.
{exp:nsm_channels:group_entries_by group_by="entry_date format='%Y, %M'" } {if group_count == 1}
Total number of groups being displayed: {group_total_results}
Total number of entries being displayed for all groups: {group_channel_entries_total_results}
Group Count: {group_count}
Total number of entries being displayed for this group: {group_channel_entries_total_results}
Testing that this is the end of the list
{/if} {/exp:nsm_channels:group_entries_by}