The best place to look at for such queries is the COBOL manual.
From the good old Language Reference:
ZERO, ZEROS, ZEROES
Represents the numeric value zero (0) or one or more occurrences of the
character zero, depending on context.
When the figurative constant ZERO, ZEROS, or ZEROES is used in a
context that requires an alphanumeric character, an alphanumeric character
zero is used. When the context requires a national character zero, a
national character zero is used (value NX'0030'). When the context cannot
be determined, an alphanumeric character zero is used.
Alternative spellings ZEROS and ZEROES for ZERO
Which is clear enough in itself.Edit
: My bad Robert; didn't see you'd already replied to the post.