A CRM migration script can finish without errors and still move customer and sales data incorrectly. The migration log telling you it succeeded is not the same as the data actually being right, which is why this needs its own dedicated testing pass.
Confirming that source and destination have the same number of records per object type is a useful sanity check, but it says nothing about whether individual fields migrated correctly. Treat it as step one, not confirmation that the migration worked.
Custom fields, picklists, and relationships between records (contacts to accounts, deals to contacts) are the most common place migrations silently lose or misplace data. Spot-check a representative sample of records across every object type, not just the simplest ones.
Rules, triggers, and workflows that depended on the old data structure or field names can break quietly after migration, continuing to run but producing wrong results instead of failing visibly. These need to be re-tested against the migrated data, not just the migration itself.
Letting a small group of actual CRM users work in the migrated system before the full switch surfaces problems that structural data checks miss: a report that looks wrong, a filter that no longer matches, a dashboard with the wrong numbers.
However careful the testing, having a verified way to revert to the source system if something is found post-cutover is what turns a serious migration problem into a manageable one.
Talk to our QA team about CRM testing and migration validation.