24a Letter: short one tucked inside document. ??a???t?r
Character fits and would be a letter. A charter might be a document but can't see how ac works.
If correct then 24d Accessing container , Irish terrier would be c?i?? but I've no idea.
28a Mentioned , general design t?t???? Fifth letter is e if 14d is correct "Number left that goes into ten, almost. T?e?t? o?? Twenty one fits and is a number but can't see rest of it.
Thanks