Thanks so much Liz. Yes, confirmation of Dorothy's birth would be a great starting point. If we can get confirmation 1. of her date of birth, we might have a better chance of finding out who she is living with in the 1911 census. 2. of her mother's name to help tie her back to Edward and Catherine Comish/Comaish.
Dorothy was illegitimate - I don't know how it worked in IOM, but in Scotland although a child was/is illegitimate, if the father and mother BOTH attended the registration, the child could be registered under the father's surname, but if only the mother registered the birth, the child HAD to be registered under the mother's surname.

Dorothy's marriage cert in 1939 has no father noted.

NB the addresses I have for the Thomas Cain family in the early part of the 1900s are:
1911 census - 33 Hope Street
June 1917 - 26 Hope Street
Jan 1927 - 91 Hillside Avenue, where I think they lived at least till Thomas' death.

Your help is really appreciated.

Ellen