I assume you are speaking of 1Cor 15:11 where Paul says, "thus we preach"? (or "so we preach" or something along those lines). If so it is pretty clear that when he says "we" he speaks of himself and the other apostles. If in this passage, by his usage of graphe, he does not mean "Scriptures", (as in the Tanach), but rather simply means "writings", then the whole passage comes perfectly into view, (for those willing to see it), for he speaks not of prophecies in the Tanach concerning Messiah herein but rather speaks concerning the Good News or Gospel histories which were already being circulated, (I know that mainstream Christianity, and especially the hard-core grace minded Paulines, will fight what I say tooth and nail here: but he went up to learn the "historie(s)" from Kephas according to Gal 1:18 and yet only needed to spend fifteen days going over what he received, (because what he received were written documents, writings, "graphas", which he could take and walk through with Messiah on his own)). Look at what comes just before this section in the previous chapter:
1 Corinthians 14:36 - 15:11
36 What? was it from you that the Word of Elohim went forth? or unto you alone did he come?
37 If anyone thinks himself to be a prophet, or spiritual, let the same recognize the things I write to you, that they are the commandments of the Master.
38 But if anyone is ignorant, [or ignores] let him be ignorant.
39 Wherefore, my brethren, desire earnestly to prophesy, and forbid not to speak in foreign tongues.
40 But let all things be done decently and in order.
01 Now I declare to you, brethren, the Good News which I preached to you, which also you received, in which you also stand:
02 By which you also are being delivered, if you hold firmly the word which I preached to you--unless you believed in vain.
03 For I delivered to you first of all that which I also received: [Gal 1:18] that Messiah died for our sins according to the writings:
04 And that he was buried, and that he was raised on the third day according to the writings:
05 And that he appeared to Kephas, then to the twelve.
06 Then he appeared to over five hundred brethren upon one occasion, most of whom remain until now, but some have also fallen asleep.
07 Then he appeared to Yakob, then to all the apostles:
08 And last of all, as if a miscarriage, he appeared to me also:
09 For I am the least of the apostles, who is not worthy to be called an apostle, for that I persecuted the congregation of Elohim.
10 But I am what I am by the grace of Elohim: His grace which was bestowed on me was not futile, but I labored the more-abundantly-so than all of them, yet not I, but the grace of Elohim which was together-with me.
11 Whether then it is I or they, [the other apostles] thus we preach, and thus you believed.