First of all, Congratulations!
I think its great that you have good news five years after diagnosis.

However; it was always been my understanding that benign MS was considered after 10 years of no increased disability.

I was diag in 2002. So far so good and my MRI's have not changed. I too inject beta 1b.
My MRI's were really bad and the doc couldn't believe I was the same person standing before her with such a bad MRI.
So, some people show lots of lesions and very little symptoms and some people show few lesions with major symptoms.

MS...the snowflake disease....no two cases are exactly alike.