In the siddur and machzor, when quoting scripture, the text will sometimes introduce the pasuk with "נאמר", meaning "it is said". Other times the pasuk will be introduced with "כתוב", meaning "it is written". Variations of these roots are also used. Sometimes no introduction is made at all.
When there's more than one pasuk, the typical quoting structure seems to start with ככתוב and then continue with ונאמר. However, this structure is frequently disrupted (see Musaph for Rosh HaShana), furthermore the difference in meaning between "said" and "written" is striking. The introductions are also seemingly interchangeable when only one pasuk is quoted.
Is there a meaningful difference between the scripture introductions beyond the text structure, and if so, what is it?