They are different models. To be honest - and i know this is gonna sound odd - but i am not even sure which ones they are.
Sad i know - but I log all my watch purchases, battery changes etc (Yup i know the regularity of battery changes for most Seiko movements), if i sell, or modify etc. Each watch has its own A4 page which are kept in serial number order. When slotting a new purchase in the folder, i noticed that it had the same s/n as the proceeding one. Now i will just have to find the watches in question