Regarding the record you have seen: It records that he died - (not necessarily on the voyage). The remarks in the left margin have been added at some later date to the indent. You can see which convicts had escaped, and who were pardoned, and who had died. Solomon died 16 July 1791, about 1 year after arriving in NSW. So the margin notes were made after that time.
Reverend Richard JOHNSON who kept the births, death and marriage register of the colony noted in the “Register of Burials at Sydney Cove” that on 16th June 1791, he had buried “Solomon Bockron, convict, a jew”. This was Solomon Bockerah, thought to be one of the few Sephardic Jews to be deported to Australia.
(The Register of Burials at Sydney Cove is in the Mitchell library.)
When looking at NSW BMD online, there are 2 available records for him - note spelling.
BOCKRON SOLOMON 321/1791 V1791321
BOCKROW SOLOMON 297/1791 V1791297