Welcome to Microsoft Q&A platform and thanks for posting your question here.
As I understand your query, you are trying to copy data for multiple files from past few years. The issue here is that few of the files are having semi colon delimiter and few are having tab delimiter . Pipeline is not working in generic way. Please let me know if that is not the ask here.
In order to handle this scenario, you need to parameterize your dataset for column delimiter option and pass the value during the runtime.
If your files are separately stored in year wise folders, then make sure to filter out the files from 2016-19 and pass ';' delimiter during the runtime and similarly for files from 2019 onwards, pass '/t' during the runtime.
You can use copy activity too instead of dataflow to achieve this requirement as there is not much transformation for this use case.
Hope it helps. Kindly accept the answer if it's been of help, else kindly revert back on thread having additional queries. Thanks