There is an "intial" sealing and a "final" sealing which coincides with the angels letting loose the winds from the four corners (Revelation). The WTS always leaves itself an out.
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w97 8/15 pp. 14-15 Living for Today or for an Eternal Future? ***Consider the text at Revelation 7:1, 3, which says that the "four winds" of destruction are held back "until after we have sealed the slaves of our God in their foreheads." This is not referring to the initial sealing, which takes place when those of the 144,000 receive the heavenly calling. (Ephesians 1:13) It refers to the final sealing, when they are irrevocably identified as tried and faithful "slaves of our God."