Could a 163-bytes size difference between the tgz of two different 590mb dirs be caused just from file metadata? Or is the file data diff?

While trying to remove duplicates of MRI readings I am tarring / compressing (**tgz**) the top-level directory with a mix of executables, pdf, text, dll, and data in proprietary format (but sometimes with different "last modified" dates). Any tgz files with same byte-size, I consider duplicate MRI scans. I am comparing 10+ MRI datasets that have been stored in a variety of compression formats in local and cloud drives for 10+ years. I'm sure some are duplicates. > tar cfa mri01.tgz MRI01 > tar cfa mri02.tgz MRI02 For datasets that are, before tgz compression, typically about 615-mb with about 135 files, I sometimes see no size difference, a size difference of only 150-bytes or so, and significant size differences in the tgz files. I don't know what to think. Could a 150-byte size difference between the tgz of such large datasets be caused just by file meta-data, like "last modified date"? Or, does such a tiny size difference indicate these are different MRI scans? Is there a better way to detect duplicates of this type of data?