US taxes after returning from Japan

As a US citizen in Japan, I file my taxes and exemption form every year, but I know a lot of people don't bother or even know that have to. For people who returned after living in Japan for a few years, did the IRS contact you or did you have a penalty when you started filing again? I have friends returning this year who haven't filed in years, and we're wondering if they should prepare for an audit or have copies of their contracts showing they were earning abroad and thus exempt.

As long as you don't make over a certain amount, $100,800 for 2015, you don't have to pay US income taxes (US citizen). You're supposed to file if you make over $10,300. However, for full years of earning abroad, with none earned in the US, as along as I never went over the limit, I didn't file and was never bothered by the IRS even when I started refiling upon return. For many working overseas, obtaining the forms is near impossible; not everywhere has net access.

Save your pay stubs if you're getting paid by an employer to show you were outside the country just in case. However, there would be no US employer to turn in a W3 to give them any cause to even know you existed that year, so I don't think the IRS would find any red flags. You might need a bit more paperwork if self-employed.

Thanks!