YOU SAID:

The dog had had ten previous owners

INTO JAPANESE

犬の飼い主は10人いた

BACK INTO ENGLISH

There were ten dog owners

INTO JAPANESE

犬の飼い主は10人いました

BACK INTO ENGLISH

There were 10 dog owners

INTO JAPANESE

犬の飼い主は10人いました

BACK INTO ENGLISH

There were 10 dog owners