Yeah they dun exactly know....but if u are "LUCKY" enough and kena suspect from the TAX dept...u better have all the proper documents ready to answer to them....else the backdated taxes that u r going to pay if gonna cost you a bomb Ppl actually lose half or more or even all of their assets becoz of this.
Btw...if u r lucky enuf....when come to title transfer especially when u wanna transfer to your wife/kids/etc or after you are dead will also be a big prob if the tax dept suspects you

So dont pray pray