How often has the ISO standard been updated it first appeared in $1987?$

ISO attempts to review each of its standards every $5$ years, but has actually issued revisions every $3$ years.

ISO attempts to review each of its standards every $5$ years, but has actually issued revisions every year.

ISO attempts to review, each of its standards every $5$ years, but has actually issued revisions every $6$ to $8$ years

ISO attempts to review each of its standards every $5$ years, but has actually issued revisions every $10$ to $12$ years.