Depends somewhat on how you are defining the OT (do you mean, everything before the gospels, or do you mean everything before His "death"?) Do you mean, could the apostles preach anything from what they experienced when Jesus walked this earth? Do you mean, could Paul have received revelation directly from the risen and ascended/exalted Christ, to disclose (in written form, what we see now in the epistles)? I'm not sure which you might be thinking... But here's something I'd posted awhile back...
for your consideration:
[quoting]
Acts 3:21 [speaking to "ye men of Israel," v.12 (unsaved persons as noted in v.13-15,17,19)] then states: "whom indeed it behooves heaven to receive until the times of restoration of all things of which God spoke by the mouth of His holy prophets from the age." [in contrast to that which He had theretofore kept "hidden in God"/was as yet undisclosed]
In vv.13 and 26 the phrase "His Servant Jesus" (they had not been expecting the "suffering servant" aspects of His Person, only the "reigning-in-power King" aspects, though both aspects had been prophesied in the OT); chpt 3's point is Peter telling them they'd overlooked the former of these two aspects, and thus had a hand (themselves) in fulfilling that very thing, vv.13-15, but this was not saying that "everything" was at this point in time (the time of Acts 3) fully fulfilled; and...
...there are TWO "raise" senses spoken of in Acts 3... v.15 speaking of His being "raised from the dead," but the other being "raised" to a position of prominence BEFORE His death (that is, to the position of 'a Prophet like unto Moses'...'raise up unto you of your brethren like unto me [/Moses]; him shall ye hear in all things whatsoever he shall say unto you' and 'UNTO YOU FIRST God, having raised up [to a position of prominence BEFORE His death] His Servant Jesus, SENT him to bless you, in turning away every one of you from his iniquities'). The "ALL things which God spoke by the mouth of His holy prophets" (meaning, OT prophecies) have not yet been fully fulfilled, but remain for a yet-future time (and I believe Joel is one such prophecy).
The word "King" is only used [re: Jesus] TWO times in all of the epistles, and both of them are "future" [see Rev19:15b still speaking in "future tense"], 1Tim6:15 being one of those, says, "which IN HIS TIMES He SHALL SHEW [openly manifest], who is the blessed and only Potentate, the King of kings, and Lord of lords"
[end quoting]
____________
I think that Ephesians 3:5 is something to consider along with this:
"5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit"... this phrase [used together like this] "apostles and prophets" can only mean "the NT apostles and prophets"
for your consideration:
[quoting]
Acts 3:21 [speaking to "ye men of Israel," v.12 (unsaved persons as noted in v.13-15,17,19)] then states: "whom indeed it behooves heaven to receive until the times of restoration of all things of which God spoke by the mouth of His holy prophets from the age." [in contrast to that which He had theretofore kept "hidden in God"/was as yet undisclosed]
In vv.13 and 26 the phrase "His Servant Jesus" (they had not been expecting the "suffering servant" aspects of His Person, only the "reigning-in-power King" aspects, though both aspects had been prophesied in the OT); chpt 3's point is Peter telling them they'd overlooked the former of these two aspects, and thus had a hand (themselves) in fulfilling that very thing, vv.13-15, but this was not saying that "everything" was at this point in time (the time of Acts 3) fully fulfilled; and...
...there are TWO "raise" senses spoken of in Acts 3... v.15 speaking of His being "raised from the dead," but the other being "raised" to a position of prominence BEFORE His death (that is, to the position of 'a Prophet like unto Moses'...'raise up unto you of your brethren like unto me [/Moses]; him shall ye hear in all things whatsoever he shall say unto you' and 'UNTO YOU FIRST God, having raised up [to a position of prominence BEFORE His death] His Servant Jesus, SENT him to bless you, in turning away every one of you from his iniquities'). The "ALL things which God spoke by the mouth of His holy prophets" (meaning, OT prophecies) have not yet been fully fulfilled, but remain for a yet-future time (and I believe Joel is one such prophecy).
The word "King" is only used [re: Jesus] TWO times in all of the epistles, and both of them are "future" [see Rev19:15b still speaking in "future tense"], 1Tim6:15 being one of those, says, "which IN HIS TIMES He SHALL SHEW [openly manifest], who is the blessed and only Potentate, the King of kings, and Lord of lords"
[end quoting]
____________
I think that Ephesians 3:5 is something to consider along with this:
"5 Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit"... this phrase [used together like this] "apostles and prophets" can only mean "the NT apostles and prophets"