"was previously planned" is correct and usable in written English.
It is typically used to indicate that something was planned before a particular point in time. Example: The concert, which was previously planned for next month, has been postponed due to the COVID-19 pandemic.
The increase was previously planned for April 2020.
When arguing about budgets, for example, they use the word "cut" to mean "spend less than was previously planned".
There is also a new plan to open a campus police substation until construction ends on one that was previously planned.
To deliver what was previously planned, three main drivers must be in place: quality of the scope definition; alignment of the business strategy; and operability of the asset delivered.
The House plans to vote Friday on a resolution of approval (where a "yes" vote means yes to the deal) instead of a resolution of disapproval (where a "yes" vote means no to the deal) that was previously planned.
If any members of the family travel by train you'll cheer at the news that rail-price increases will by capped at inflation, rather than inflation plus 1 per cent, as was previously planned.
Digg just announced on its official blog that it was previously planning on building a reader in the second half of 2013.
Moscow said the exercises were routine and had been previously planned.
A half-dozen ferry terminals that were previously planned along New York Harbor have been put on the fast track.
Morrison said the new package would affect fewer people than the pension indexation changes that were previously planned.
The statement continued: "Regarding helicopters, there were previously planned repairs of military equipment delivered to Syria many years ago".
