Early work on deciphering the Indus script (which still has not been acceptably deciphered) was done by Hunter in his 1934 Ph.D work at Oxford - https://ufdc.ufl.edu/AA00013642/00001
Mahadevan's Indus Concordance is one of the standard works in this field.
Yet, when I compared the signs in Hunter's thesis with the signs in Mahadevan's Concordance, I found that many of Hunter's signs were absent from the Concordance. I did see some similar-looking signs in the Concordance, but some other signs were totally absent, though a few of Hunter's signs were indeed present in Mahadevan's Concordance.
Why would Hunter's signs be missing from Mahadevan's Concordance?