There's a difference in having the gift of prophecy in the context of predicting future events or a prophet that declares glad tidings and good news from a divine source.
it-2 p. 694 Prophet
The Greek pro·phe′tes literally means “a speaker out [Gr., pro, “before” or “in front of,” and phe·mi′, “say”]” and thus describes a proclaimer, one who makes known messages attributed to a divine source.
The original etymology of the Greek term for a prophet can be found in a Greek Lexicon:
Prophetes - Greek Lexicon
http://www.studylight.org/lex/grk/view.cgi?number=4396
1. In Greek writings, an interpreter of oracles or of other hidden things
2. one who, moved by the Spirit of God and hence his organ or spokesman, solemnly declares to men what he has received by inspiration, especially concerning future events, and in particular such as relate to the cause and kingdom of God and to human salvation
e. of men filled with the Spirit of God, who by God's authority and command in words of weight pleads the cause of God and urges salvation of men
The Watchtower Society has been more definitive (especially in later years) about the concept of prophecy and how it applies to them. Those who label them false prophets generally disagree with their overall message. You can still disagree without placing some sort of label on them. Their predictions about the future always revolved around Armageddon. This seems to be the real issue to people; more so than a mistaken viewpoint about when specifically it will actually come.