Превод - Японски-Английски - 被告からの反論は、１原告が名簿を盗み、これによって被告（当方）が相当損害を被、...

counter-arguments
may be in the singular: I was guessing there were more than 1

I think the number 1 in the text refers to "Point 1" or "Item 1" in the previous translation I did for the same requester

(our client)
may be
(i.e. we)

received considerable injury
does not mean, of course, "physical harm," but only "professional problems that he then had to overcome"