It is a great question to ask JWs. "Show me where in the Bible can 1919 be established"
From the JW library the significance of 1919 includes the following but has been subject to various 'new light'. Keying the words "1919 calculation" into the search section provides this information -
1919, 1,260 days begin (Re 12:6, 14): re 183-184
1,290 days begin (Da 12:11): dp 300; w93 11/1 10-11
144,000 begin “singing as if a new song” (Re 14:3): re 200
antitypical Festival of Booths resumes: w96 7/1 24
Babylon the Great falls (Re 14:8; 18:2): re 205-206, 209, 259-261; w89 5/1 3-5; w88 12/15 20-21
birth of new nation (Isa 66:8): re 183-184; ip-2 397-400; w94 1/15 14
‘disgusting thing placed’ (Da 12:11): dp 300; w93 11/1 10-11
“faithful and discreet slave” ‘appointed over master’s belongings’ (Mt 24:47): w04 3/1 12; wt 131
faithful slaves ‘appointed over many things’ (Mt 25:21, 23): w04 3/1 17
‘fire hurled to earth’ (Re 8:5): w09 1/15 32; re 131-132
‘four angels untied’ (Re 9:15): re 149-151; w88 12/15 13
“harvest of the earth” begins (Re 14:14-16): re 211-212
Jehovah’s chariotlike heavenly organization gets in touch with Ezekiel class (Eze 1): w91 3/15 11
Jehovah’s spirit begins to be poured out on remnant (Joe 2:28, 29): w98 5/1 14-15
“key of the house of David” placed on shoulder of remnant (Isa 22:22): w09 1/15 31
locusts swarm from abyss (Re 9): re 143-148; w89 4/1 17-18; w88 12/15 12-13
“opened door” set before remnant (Re 3:8): re 60-65
remnant “come quivering to Jehovah” (Hos 3:5): w91 8/15 17
remnant eat “little scroll” (Re 10:8-11): re 159-160
remnant figuratively resurrected: dp 290-291; w88 10/15 13; w87 7/1 21-23
remnant freed from Babylon the Great: ip-2 74; ip-1 400-401; w89 5/1 4-5
remnant ‘hold possession of land’ (Isa 60:21): w02 7/1 18; ip-2 319-320
remnant refined (Isa 1:24-27): ip-1 32-34
remnant restored to spiritual paradise: ip-1 380; w91 5/15 16
remnant step before “waters” of mankind (Jos 3:15-17): w86 12/15 13
two witnesses resurrected (Re 11:11, 12): re 169-170
virgins hear cry, “Here is the bridegroom!” (Mt 25:6): w04 3/1 14
“Way of Holiness” opened (Isa 35:8): ip-1 380-381; ws 132-134
“your God has become king” begins to be declared (Isa 52:7): ip-2 187