I open a model in R2009b,11b,12b and accessing the models(updating diagram/genrating code/simulating the model/ debugging the .m/.tlc files by putting break points). But I didn't face any issue. How matlab is taking care of this situation. I was expecting some kind of crash, because the same file is used across the versions. However in one file i kept break point. It's in debugging mode. The another is running with out break point... I use different workspace variables across the versions. But still everything works .