Patents: Incorrect Inventorship on a Patent

I worked as a consultant for a company several years ago. During the period I agreed to assign the rights to any invention to the company (The assignment agreement is now expired). I had several inventions during this period. These inventions have recently been published as USPTO patent applications, attributed to other employees of the company. However, I am not named as an inventor and I have documentation relating to the conception of the inventions. At the minimum I would like to be named inventor. However, I don't want to give up any rights that I may not know about. The plan is to draft a letter to the company myself and request that I be added as an inventor. Should I consult an attorney first or have them write the letter on my behalf? Are there any rights that I may have to the inventions?