For their sample period,monthly expiration dates were available up to 18 months into the future

For their sample period,monthly expiration dates were available up to 18 months into the future
For their sample period,monthly expiration dates were available up to 18 months into the future

For their sample period,monthly expiration dates were available up to 18 months into the future
采样期间,有效期可长太（未来的）18个月
这里into the future不译出即可,因为18个月,已经含有未来的意思了

对于他们的样本期间，每月到期日期是可长达18个月到未来