@ vfr
Earlier this week I was at Bell facility in Mirabel: I had a chat with the chief of flight testing and a bunch of FT guys... they all new the (evident) meaning of the first number but nobody could really explain the other two digits... but I tend to agree with you that probably the second digit recalls a change of design and the last one is a sequential chronological number related to the model (maybe)...
Still there are can be many objections to my interpretation...