Taiwan’s official rules on addressing envelopes (wàiwén yóujiàn dìzhǐ shūxiě yuánzé), as issued by the Ministry of Education, were changed very recently.
Here’s the previous style:
(yī) dì-yī háng: xìngmíng (huò shāngdiàn, gōngsī děng), lìrú: FAN, Kai-Lang
(èr) dì-èr háng: ménpái hàomǎ, lòng, xiàng, duàn, lù jiēmíng, lìrú: No.55, Lane 77, Sec.2, Jinshan S. Rd.
(sān) dì-sān háng: xiāng-zhèn, xiàn-shì, yóudì qūhào, lìrú: Jinshan, Taipei County, 249
(sì) dì-sì háng: guó míng, lìrú: Taiwan (R.O.C.)
And here’s what the new rules give:
(yī) dì-yī háng: xìngmíng (huò shāngdiàn, gōngsī děng), lìrú: Fan Kailang
(èr) dì-èr háng: ménpái hàomǎ, lòng, xiàng, duàn, lù jiēmíng, lìrú: 55, Ln. 77, Sec. 2, Jinshan S. Rd.
(sān) xiāng-zhèn, xiàn-shì, yóudì qūhào, lìrú: Jinshan, Taipei County 10603
(sì) dì-sì háng: guó míng, lìrú: Taiwan (R.O.C.)
So, no change in the placement of “Sec.” But at least there’s now a space after the abbreviations, “Lane” can become “Ln.”, the officially encouraged style has the 5-digit postal code, and there’s no comma before the postal code. And “No.” is no longer mandated. And, of course, personal names are handled differently (though the exact style is still up to the individual).
As far as real-world situations go, however, people can probably put the section number pretty much anywhere and have the letter get through. So go with whatever makes ya happy.