Are tax returns vital for (London) K-1 interview/I-134?
 

I'm quite sure this point has been raised b4,but am I right in assuming that the employer's letter and bank statements are sufficient when presenting the I-134 at the K-1 interview? My co-sponser has a respectable job (teacher for over 10 years) and a healthy bank balance,so surely this will be enough? I don't want to hassle my co-sponser any more than I have to by asking them to get me tax returns if they're not necesarry (I know I need them though for the I-864/AOS.