Winter of 1699, Lemuel is being searched in Lilliput.
 Indeed, that secret pocket wasn’t discovered by the two officers who searched Gulliver in Lilliput, (three years before this chapter was written) and his condom was undetected.
I guess Gulliver was hesitant to let the Lilliputian officers see his condom, as they would’ve quite surely confiscated it. They were likely to suspect that Gulliver would use it to kidnap the Emperor for ransom. Mary writes all about in Chapter Twelve.