Please add both spellings of "grandad" (you accept granddad but not grandad). https://www.quora.com/Which-is-the-correct-spelling-granddad-or-grandad-and-why
Yes, indeed they should both be accepted. Here's a bit of statistics from Ngram attesting to the same thing. According to Google NGram, in British English the spelling "grandad" is more popular than "granddad", however American English, the spelling "granddad" is more popular than "grandad".
Both are now included as the correct spelling. Thank you for the notification.