The data team has eight maintenance requests to finish in its sandbox. Each exercise starts a fresh session, so changes from another request are not available. The source fixtures vary on the hidden check copy. Build tables from queries, use stable customer keys and keep the requested subset explicit.
Some tasks change stored data; others only read a retained version. The difference matters. A SELECT can show the correct old value while leaving the damaged table unchanged. When the task asks for a repair, the checker reads the target table afterward. A sandbox clone also has an independent life: changing it must not change the source that other reports use.