If you use the OS 3.9 SDK to compile an application which uses only functions contained in OS 1.3, then it will run on anything from 1.3 to 4.1 and MorphOS.
I am not sure if the 1.3 SDK is compatible with 4.0+.
Note that to compile a program to run on OS 1.3, you need a compiler which has a 1.3-compatible link library. Dice C has such, for example. Code compiled with VBCC does not run on OS 1.3.
For example, if I were to write a simple application using the intuition libraries for OS 1.x and then attempted to compile this for OS 4.x would it work correctly?
You shouldn't do this. Coding style has changed between 1.3 and 2.0 and again in 3.0 and 3.5. You should not use 1.3 style when writing native programs for OS 4. Although it should work.
