Hi Denise,
Make sure any margin instruction is clear to the typesetter if there is any potential confusion, e.g. centre all headings.
In general, any incorrect text in the same line of text but separated by correct text, should have a corresponding margin mark. This is obvious in the case of different types of error but if there are similar errors, such as lower case initial letters instead of capitals then ‘caps x 3’ might be appropriate as long as all three errors have an appropriate text mark to indicate what needs to be changed.
Dick