I just ran a search on the phrase in a number of different Bible translations. It does not appear in most modern Bible translations at all, and that includes the NWT. It does appear at 2 Peter 1:12 in the KJV and the New King James. Other translations render the verse in a way that does not imply 'the truth at the present time,' but seem to refer to the truth being present in Christians.
The NASB, for example, reads, "Therefore, I will always be ready to remind you of these things, even though you already know them, and have been established in the truth which is present with you."
The ESV (English Standard Version) reads: "Therefore I intend always to remind you of these qualities, though you know them and are established in the truth that you have."
Even the NWT reads, "For this reason I shall be disposed always to remind YOU of these things, although YOU know [them] and are firmly set in the truth that is present [in YOU]."
Clearly the emphasis of the verse is on the truth being present in believers, and not on the believers' having to keep up with ever-changing versions of the truth.