question about IBIS versions

I have a situation where an IBIS model that was made with s2ibis2, and
is therefore ostensibly a Version 2.1 model, may need a model selector
keyword.

The question is: is changing the version to 3.x and adding the model selector
sufficient, or are there actual changes in the syntax of stuff that's common
between 2.1 and 3.x?

Or are there any other pitfalls in what I'm attempting here?

-- 
Kim Helliwell
Senior CAE Engineer
Acuson Corporation
Phone: 650 694 5030  FAX: 650 943 7260