Not all scarabs bearing a royal name are contemporaneous to the ruling pharaoh. Some kings were held in particularly high regard, and thus their name appears on scarabs hundreds of years after their reign. Thutmosis III of Dynasty XVIII was particularly honoured in this way, with his praenomen, Men-Kheper-Re, used on scarabs for a period of circa 1000 years.
To find out more about Ancient Egyptian amulets please see our relevant blog post: Egyptian Amulets and their Meanings.