bldgdesign...the major codes (IBC, UBC, SBC) are/were all "model codes". A municipality, county, or state, unless directed otherwise by state law, has the option of (a)adopting the model code "as is", (b)adopting the model code with modifications, or (c) creating their own code. Most will do either (a) or (b).
Codes are not automatically adopted with each new edition, unless some ordinance or law dictates (Florida has such a law). That is usually done by local ordinance, proclamation, or state law. Further, there's nothing that requires a locality to adopt the latest version of the code. As an example, in my area, the 1997 Standard Building Code was adopted at about the time the 1999 code came out. The 1999 code was not adopted and both were superceded when state law required the adoption of a state building code, which is now mandatory and automatically set in place with each new edition.
You will need to do a little ordinance/law research in the locality of the code application to check your situation.
If you are in an area that has a statewide building code (Florida, NC, VA, CA, etc.)then adoption might be automatic. If not, then you will have to check to see if adoption was done and if so, when it took effect and to which code version it referenced.
In the absence of specific adoption, it is likely you can revert to accepted practice in the area. Most architects will know this for a given area.
