今年有報稅所以保險起見再確認了一下ITIN有沒有過期，IRS的Q&A裡面寫得蠻清楚的
Q1: Which ITINs are subject to expire at the end of 2020?
A1: ITINs that have not been used on a tax return for tax years 2017, 2018 or 2019 will expire December 31, 2020. Additionally, ITINs with middle digits 88 (For example: 9NN-88-NNNN) will expire December 31, 2020. Those with middle digits 90, 91, 92, 94, 95, 96, 97, 98 or 99, that were assigned before 2013 and have not already been renewed, will also expire at the end of this year.
Q2: Which ITINs will NOT expire?
A2: Any ITIN that does not have a middle digit of 88, 90, 91, 92, 94, 95, 96, 97, 98 or 99 and was used on a tax return for tax years 2017, 2018 or 2019 will not expire in 2020.
Q2的部分跟原本的認知相同，最慢每三年要報一次不然ITIN會失效 (有報2017年份的稅，ITIN在2020年份的稅就還不會到期，所以2021可以報2018-2020的三年份的稅)
Q1提到2013年以前申請的(可以看ITIN中間的數字判斷)都會在今年到期，目前根據IRS的說明看起來2013之後申請的ITIN只要有定時報稅都不會失效
但是基本上都是三年報一次，怕中間政策可能有變動，最好在報稅前再確認一下
資料來源：
1. https://www.irs.gov/individuals/itin-expiration-faqs
2. https://www.irs.gov/individuals/individual-taxpayer-identification-number
3. https://www.irs.gov/pub/irs-pdf/p5259.pdf
