Yes it is normal that helicopter type ratings are only valid one year even if it is only for PPL use.
Fixed wing guys have class ratings like SEP (Single engine piston) and for PPL the class rating is valid 2 years and they need to fly 12 hrs the last 12 months.
If I remember correctly you only need to renew you type rating on one piston helicopter and if you have flown the other type at least 2 hrs within the validation period then that renews your LPC on that to. You need to ask your examiner or licensing authority about that!