According to the Watchtower Society, there are "abundant credentials" that the Faithful and Discreet Slave has been around since Noah's day. You can find this list in the March 1, 1981 Watchtower, p.27 (I've highlighted some of the more laughable ones):
(1) Noah’s wife, Gen. 7:7; (2) angels sent to Lot, Gen. 19:15; (3) Rebekah, Gen. 24:64; (4) Joseph and Benjamin, Gen. 45:14; (5) gleanings left behind, Lev. 19:9; (6) two spies to Rahab, Josh. 2:4; (7) Barak, Judg. 4:14; (8) Jephthah, Judg. 11:34; (9) Naomi and Ruth, Ruth 2:2; (10) David’s Israelite warriors, 2 Sam. 18:1; (11) Jehu, 2 Ki. 10:11, 15; (12) Mordecai and Esther, Esther 4:13; (13) Job, Job 42:10, 13; (14) King’s daughter, Ps. 45:13; (15) men of loving-kindness, Ps. 50:5; (16) intimate group, Ps. 89:7; (17) Shear-jashub, Isa. 7:3; (18) light of the nations, Isa. 60:3; (19) big trees of righteousness, Isa. 61:3; (20) ministers of our God, Isa. 61:6; (21) cluster preserved, Isa. 65:8; (22) servants called by another name, Isa. 65:15; (23) men trembling at God’s word, Isa. 66:5; (24) new nation born, Isa. 66:8; (25) Jeremiah, Jer. 1:10; (26) Jehovah’s people in the new covenant, Jer. 31:33; (27) enduring watchman, Ezek. 3:16-27; (28) man in linen, Ezek. 9:2; (29) cleansed people, Ezek. 36:29-32; (30) dwellers in center of earth, Ezek. 38:12; (31) the host of heaven, Dan. 8:10; (32) sanctuary restored (cleansed), Dan. 8:14; (33) they that are wise, Dan. 11:33; (34) the happy one who is keeping in expectation, Dan. 12:12; (35) all flesh receiving the spirit, Joel 2:28; (36) Jonah, Jon. 3:1-3; (37) apple of Jehovah’s eye, Zech. 2:8; (38) liberated remnant, Zech. 2:7; (39) a Jew, Zech. 8:23; (40) sons of Levi, Mal. 3:3; (41) wheat, Matt. 13:25; (42) sons of the kingdom, Matt. 13:38; (43) workers for the vineyard, Matt. 20:1; (44) those invited to marriage feast, Matt. 22:3-14; (45) chosen ones, Matt. 24:22; (46) eagles, Matt. 24:28; (47) faithful and discreet slave, Matt. 24:45; (48) discreet virgins, Matt. 25:2; (49) brothers of the king, Matt. 25:40; (50) little flock of sheep, Luke 12:32; (51) beggar Lazarus, Luke 16:20; (52) sheep in “this fold,” John 10:1-16; (53) branches of the vine, John 15:4; (54) royal palace of David, Acts 15:16; (55) heirs with Christ, Rom. 8:17; (56) the remnant, Rom. 11:5; (57) branches in the olive tree, Rom. 11:24; (58) holy ones or saints, 1 Cor. 6:2; Rev. 16:6; (59) temple, 1 Cor. 6:19; (60) new creation, 2 Cor. 5:17; (61) ambassadors for Christ, 2 Cor. 5:20; (62) congregation of God, Gal. 1:13; (63) part of Abraham’s seed, Gal. 3:29; (64) Israel of God, Gal. 6:16; (65) body of Christ, Eph. 1:22, 23; (66) soldiers of Christ Jesus, 2 Tim. 2:3; (67) house under Christ, Heb. 3:6; (68) holy priesthood, 1 Pet. 2:5; (69) holy nation, 1 Pet. 2:9; (70) association of brothers, 1 Pet. 2:17; (71) seven congregations, Rev. 1:20; (72) twenty-four persons of advanced age, Rev. 4:4; (73) spiritual Israel, Rev. 7:4; (74) locusts, Rev. 9:3; (75) two witnesses, Rev. 11:3; (76) two olive trees, Rev. 11:4; (77) seed of the woman, Rev. 12:17; (78) New Jerusalem, Rev. 21:2; (79) the bride of Christ, Rev. 22:17; 19:7; (80) Jehovah’s witnesses, Isa. 43:10.