If I may...@SonicRings is actually onto something here. There is some inconsistency in the way MB treats native tags when dealing with multiple files. In the screenshot below, I have not used any virtual tags.

Notice how the tags are treated in both the
details panel and the summary statistics.
Summary Stats<Time> collected data from all selected files and accurately added their durations.
<Size> collected data from all selected files and accurately added their sizes.
Details Panel<Time> collected data from all selected files and accurately added their durations.
<Size> however,
did not collect data from all selected files. It only took the first.
<Play Count> behaves the same as <size>...It also does not collect data from all selected files
So what @SonicRings was asking here was if there's any chance <play count> (and size) could also be made to behave like <time>. That way, his virtual tag would accurately perform his calculation.