Thanks for your post and welcome to the forums. It's great having you here involved in the Community
As mentioned by BinghamBloke, catch up is only available for 7 days. We then remove the last episode to make room for the new one.
You can catch up via ITV hub here: ITV Hub: Victoria
It's worth noting that they also only keep 4 episodes at a time.
Apologies for any inconvenience.
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