You will have to upgrade to the 2019 version before you can process 2019 wages or run the 2018 P35.

We recommend running the update as soon as possible. You can still process 2018 wages using the 2019 version by selecting '2018' in the 'Year' drop down at the top left of the Payroll screen. However, if you do not have time to run the upgrade, or wish to defer it, then there is no problem finishing processing 2018 payments using the 2018 version

If your version is higher than the instructions, this is fine. For example, 2019.03 is a later version than 2019.02, and contains all the changes of 2019.02. Every time we release a new version, we increase the version number. At the beginning of the year we often release multiple new versions, often with minor changes.