"introduced then" is correct and usable in written English
You can use this phrase when introducing two connected ideas, events, or subjects. For example: "The new policy was introduced then enforced shortly afterwards."
Finally, they were introduced, then quickly returned to the hotel.
A simple phrase -- musical or choreographic -- is introduced, then subjected to increasingly complex variations.
First, the Apple iPhone was introduced, then came Google's Android operating system.
Reforms introduced then to the EU's common agricultural policy exposed farmers to a warped version of free trade.
Conversely, if a games tax relief is introduced, then the industry will eventually enjoy annual growth of 4%.
"Our staff had a big hit when it was first introduced, then as people got used to it the situation stablilised.
In these cases, if no new charging regime is to be introduced, then either the taxpayer pays more or the infrastructure is not built.
Provocative interlopers are introduced, then quickly sent packing, leaving Elizabeth's arid existence — and the novel itself — banked aside a sea of red herrings.
Introducing the security changes, Microsoft executive Terry Myerson said that if Microsoft 10 had been introduced then many recent high-profile cyberattacks would have been foiled.
The commission suggests that it could be introduced then in a less stringent form, by including, for example, a standing charge for emergency capacity.
When top-up fees were introduced, then raised, the presence of a grants system was repeatedly used as a rationale for why the new measures would not exclude poorer students from accessing higher education.
