Use two tables. Table 1 holds your serial number field and any additional data on that customer that does not change from record to record for that customer such as their name. Table 2 holds the data that is different from record to record.
You related the two tables like this:
Table1::CustomerID = Table2::CustomerID
The classic layout design for this is put a portal to table2 on a layout for Table1 and enable "Allow creation of recors via this relationship" for Table2. This is not the only option, however.