Migration plan. - Migration scripts to take the legacy business data and ensure it is correctly defined in the data model of NS was missing.
There was no concept of data warehousing, data marts and ETL was available to facilitate this migration.
Ingestion of the old data into NS was painful. Scripts would fail multiple times and we had to re run in the middle of the nights/weekend to babysit them with NS consultants
Testing plans and training impact.
Testing plans, testing strategy, environments validation necessary to ensure no further changes were made prior to Go Live - we had to move our GO Live 5 times. Not well experienced team to formulate the correct BUT/UAT first time correctly.