The supplemental register does not provide protection the way the principal register does. One places a mark on the supplemental register if the mark is capable of functioning as a trademark, but it must develop secondary meaning before it can be registered on the principal register. After 5 years of continuous use while on the supplemental register, the USPTO will consider that prima facie evidence of secondary meaning sufficient to allow registration on the principal register (I would have to look up the 5 year term, but I believe that is correct off the top of my head). Only trademarks on the principal register are actually "registered" the way you would probably consider it, and only then can the marks be fully protected under the law.

The attorney in Maine is correct, and you should listen to him or her. Sometimes you just have to trust that an attorney knows what s/he is doing and talking about because you don't understand. I urge you to have a talk with your attorney who may be able to either explain it or provide some helpful reading materials to aid in your understanding.