And note that some countries are flexible on their requirements. A colleague and I were traveling to Singapore last year, and when we got to JFK to check in, the UA agent said that she wouldn't be able to enter Singapore because her passport expired in less than 6 months. We boarded our JFK-SFO flight not knowing if she would be able to board the SFO-SIN flight. Upon arrival at SFO, a very helpful agent in the SQ lounge called the Singaporean consulate and was told that my colleague could enter for 2 reasons, 1. (the official reason) my colleague had proof of forward travel from Singapore only 3 days after arrival, and 2. (unofficial) that this rule is used primarily to prevent vagrants from entering Singapore and not leaving.
Upon arrival in Singapore, my colleague's passport was scanned, stamped and she was allowed in with not a single mention of the expiration date being less than 6 months away (and we didn't mention it either
).
I didn't care which of the reasons was behind her being permitted into and out of Singapore, I just cared that the process was smooth!