Moving tens of thousands of records, such as contacts, projects, tasks, transactions, or documents, carries a risk of duplication. The stakes here are higher and the margin for error is smaller, so getting it wrong creates problems that could last a long time.
Here is how I approach it.
I plan before anything is touched. I do a thorough audit of all the systems or tools involved, the tools I am moving data from, and the one I am moving data into. Before a single record is exported or imported, I need to know exactly what is being moved, from where, in what order, and who is validating each section. Based on the structure of the older system and whatever the new system requires, the data to be migrated will be formatted to fit before it is transferred.
After that, I identify where duplication risk is highest before the migration begins. Going through the source data and understanding which areas are most likely to produce duplicates saves a lot of time on the other side.
I clean the source data. Standardise all fields, remove obvious duplicates, and validate critical data. The quality of what goes in determines the quality of what comes out.
Then I migrate in stages where I break the migration into sections. Move one category, validate it, fix any issues, then move to the next. This makes problems far easier to isolate.
It’s very important to validate at every stage. Check that the record count matches what was expected, that key fields have populated correctly, and that a sample of records looks right when you open them manually.
Finally, I keep the source system available in read-only mode for a defined period after migration and do not shut it down until the destination has been running reliably long enough to confirm everything is good.