Well, as far as I know, it's strongly recommended that every profile have at least one source, But that doesn't mean every profile has to have a source for every major item immediately. I have relatively few sources entered for women taking a husband's name, but in most cases this can be sourced via censuses for women who alive and married between 1850 and 1940. Sure the census could be wrong, but if so, that needs to be sourced anyway at some point. But, AFAIK there isn't any standard boilerplate for sourcing taking a husband's surname. What should it be? "Mary Roe became Mary Doe when she married John Doe? Admittedly, when I get to the stage of actually putting in the transcribed censuses instead of just referencing them, the sources will be clear, but I'm not quite to that stage yet. I'm still entering new profiles and adding the low hanging fruit (mostly censuses) as sources, but I certainly intend to add other sources when I get back around to already entered profiles. I say give people a break on such a tough item to be certain of.