Hello,
The only time you do not roll random events is when the subpath is mandatory (such as an AIT in military training). You would roll events for any Special Training subpaths (because they are optional) and suffer the -1 roll modifier that comes with it. Because OCS is also optional, you would also roll events there, taking a -2 for that. (Note: If your OCS event roll happened in the basic training phase, then OCS would get the -1 event roll modifier instead, while the Special Training gets the -2 event roll mod).
Hopefully that helps.
Thank you,
- Herbert Beas
BattleTech
Catalyst Game Labs