Strong’s #2893.
Vine’s Expository Dictionary of Biblical Words (New York: Thomas Nelson Publishers, 1985) p. 510.
The NIV note on this passage correctly informs the reader that the word "now" is not in the original Greek but that it was added to clarify that Christ's preaching was done while the people were still alive and not after they died because there are no opportunities to be saved after death. Given that the translators of the NIV (and other modern translations) follow the traditional model, the insertion of the word 'now' makes perfect sense; this is not a deliberate attempt to mislead but rather an example of the translators remaining true to their stated goal to maintain the accuracy of the translation and "its fidelity to the thought of the biblical writers." To them, Peter did not intend to teach that Christ preached to the lost after they died but this assumption is built upon a traditional foundation. It's interesting that the Universalist model does not need to adjust the text in any way.
NIV Study Bible (Grand Rapids: Zondervan, 2002) p. 1934.
NIV Study Bible "Preface to the New International Version," (Grand Rapids: Zondervan, 2002) p. xi.