The Massachusetts healthcare law requires residents to have insurance that meets minimum standards, but regulators are discovering many employers' plans test the limits by exploiting loopholes in the rules. Regulators said that reviews of scores of health plans show many cap the benefits insurers pay each year on prescription drug coverage, exclude maternity coverage for dependents, or place an annual overall dollar limit on benefits. As Congress debates an overhaul of the nation's healthcare system that would borrow heavily from the Massachusetts blueprint, any flaws in the state's system are likely to become part of the discussion, said healthcare policy specialists.