If you have TRS22, it will work with a lot of content things that older to a certain level.
But, if you have content specific to TRS22, and try to use it on older Trainz software, that is when you might have issues.
For example, if you have TS12 and try to use a locomotive specifically made for TRS22, that may not work or may have an issue. But, a lot of content for TS12, T:ANE, TRS19 will be fine on TRS22.