The problem that we have when discussing "apostasy" and "apostates" is twofold:
1 Who can lay claim to being the true inheritors of the ancient Jewish tradition that is encompassed in the OT?
2 Does the word "apostate" as understood in the the stylized patois of the Watchtower, actually occur in the OT? [There is no problem about it occurring in the NT because we know it occurs twice]
1 To suggest, as the Watchtower leadership suggests, that they and they alone can singularly wrap themselves around the mantle of the OT is not just sheer arrogance, but it spills over into the ancient Greek concept of "hubris", defined in their vocabulary as: "wanton arrogance that leads to violence against opposers, an insufferable arrogance accrued from claims to divine exclusivity" [paraphrased from Liddell and Scott Lexicon] In other words, anyone making claims of such insularity is dangerously bordering on blasphemy.
To make these claims solely on the basis of their use of the tri-syllabic mongrelized word "jehovah" which has an etymology that is neither Hebrew nor English, is puerile to say the least, especially when you consider the fact that there are several Sacred Name sects out there, most of whom are more closely linked to the OT system than the Watchtower, and whose use of Yahweh is more accurate than anything the Watchtower can match.
The Watchtower system is a proto-fascist ideal which replaces the freedom that the individual has with God, with a centrally controlled organizationally infused dynamic that supposedly serves the interests of all. Such an imperialism may be regarded as benevolent by the majority of the more somnolent of the movement, but nevertheless it is still an imposition, a manifestation of raw power. Dissenting from such systematized and institutionalized piety, is regarded as apostasy only by those cocooned in the veiled facade of Watchtower doctrinal probity.
It must also be remembered that the Watchtower leadership expresses its authority in a modern Americanized jargon with its metaphors derived from the American pop culture of the 1960s, and not from OT idiom. No Sabbath is observed, no tithes paid, and no festivals observed, all part of the warp and woof of OT cultural idiom. The Watchtower links to the OT, then, are tenuous, at best. So any "apostate" from the OT system must be a subject of interpretation, not of pre-cognitive functional subjectivity.
2 Should the word "apostate" or "apostasy" occur in the OT? The Watchtower wunderkind, Freddy Franz, whose legacy, the NW "T" is constantly being defended by his successors, certainly thought so. He introduced it 16 times in his "translation" of the OT. All these occurrences are from the Heb word "hho'neph" and its cognates. The word is clearly defined by Strong, Gesenius, and BDB as: Impiety, godlessness.
The NIV consistently translates this word as: "Ungodliness" as does the NASB. The NLT has the same.
As one can see, the use of "apostasy" in the OT, so useful to facilitating the Watchtower agenda of self-righteous posturing is entirely bogus. An "apostate" is one who has abandoned a certain regimentation which either he or his peers once regarded as "truth", while the OT word is referring to those who never had any spiritual dimension in their lives in the first place and who cared nothing about it anyway.
It is matter of scholarly debate whether the Heb vocabulary, as used in the OT had a word for "apostasy". The NASB for instance uses the word "apostasy" four times in the OT to translate the Heb "Meshubah" the meaning of which is interpretive. It can mean "faithlessness" or a"a turning away" etc, as is found at Jer 8:5. NIV has "turned away" and the NW "T" has "unfaithful" To confuse matters, Greek speaking Jews who translated the OT into the Greek LXX, used the word "apostrepso" which can mean "to return" as to an original fold, or lit, as Adam "returned" to dust. The debate continues.
The Watchtower appropriation of this word to refer to those who dissent from their structural authorization, is at least pretentious, if not, utterly mad.