Continuing where we left off last post...
We quote the gemara again [Soncino translation as always]: Our Rabbis taught: As for all the songs and praises to which David gave utterance in the Book of Psalms etc. 'To David, a psalm’ [לדוד מזמור]intimates that the Shechinah rested upon him and then he uttered [that] song; ‘a psalm of david’ [מזמור לדוד] intimates that he [first] uttered [that particular] psalm and then the Shechinah rested upon him.
The Rashbam writes מזמור לדוד - משמע מתוך המזמור באה שכינה לדוד. Does this mean that only AFTER Dovid started the Mizmor the Shechina dwelt upon him? That is clearly the implication. If so, a tremendous chiddush would emerge - Namely, that there are words of tehillim [the earlier ones in the prakim that start מזמור לדוד] that were not said with Ruach Hakodesh.
[See Rashi on Tehillim 23 who understands that the whole perek was certainly said with Ruach Hakodesh but in order to bring the Ruach Hakodesh, Dovid first heard music.]
Maybe one can suggest that the mizmor was first SUNG in which case the Ruach Hakodesh only came as he was singing but when it was WRITTEN down afterwards it was written from the very beginning with Ruach Hakodesh. Tehillim is part of Ksuvim where the kedusha stems from the WRITING [unlike nevi'im where the kedushah stems from the speech] so what matters to us was that it was WRITTEN completely with Ruach Hakodesh. See what I wrote here.
This requires further thought and research.
See מרבה עמידה of Rabbi Homnick הערה כג