In some cases, when you import contacts from a CSV file into a sequence, not all contacts from that file will be added to the sequence. This is because some of the contacts from your CSV file are already in one of your current sequences.
There are two ways to move all contacts from a CSV file into a sequence:
Via a new list on the People page.
Using the Import File Name smart filter.
Moving all contacts from a CSV file into a sequence via a new list on the People page
To do that:
Create a new list on the People page.
In the Import from CSV dialog window, select the list you created. This action moves all imported contacts to that list.
When the import process finishes, open the list, select all contacts in the list using the All in list option, and click Move to sequence. This action moves all contacts in the list, including the contacts that are currently in other active sequences.
Moving all contacts from a CSV file into a sequence using the Import File Name smart filter
To do that:
On the People page, click Add filter.
In the New smart filter dialog window, select the Import File Name property is Your File Name (see the screenshot).
Click Apply. This action filters all contacts from the selected CSV file.
Select all contacts in the list using the All in list option, and click Move to sequence.
This action moves all contacts in the list, including the contacts that are currently in other active sequences.