All right Ken. Good topic, the infamous rank subject. I personally think if you start at a new dojo you should ask that Sensei if they accept your rank. If they say yes fine, go ahead and wear that belt, if no then you need to decide whether or not to train there. At our dojo our Sensei always allows practicioners from other dojos to to wear whatever belt they have. If they can practice with the people in our dojo of the same rank at their level and intensity of training there's no problem. It's up to the practicioner to be honest with him/herself. Having said that there's no point fretting over someone elses rank, it's not a race!
All the best Jason T