You give no sources or parishes but there are very few parish regs before 1640 and significant gaps upto 1700 so for example you can never be sure of marriages which may have taken place in another parish. Land records may give an earlier sequence but here too generations can be skipped ; wills from early/mid 17th C can help but are very incomplete. There are many incorrect 'guesses' on various sites (the IGI is notorious) many merely copying the errors of others

The final e on Cowin is known elsewhere at around mid 17th C. - spellings depended on Parish Clark and could even differ in same sentence.