I have tried to read old questions but couldn't find answer.

I have a file where column A is old product number, B old name, C new
product number and D new name. Most products has 1 old and 1 new, but some
products might have f.ex. 3 new numbers. There are about 1650 rows.

I have done search to find new number based on old number like this:
=VLOOKUP(C5;'files'!A6:E1646;4;FALSE)
This works if there is only 1 new code, but how do I find if there is more?

old nr old name new nr new name
Column A Column B Column C Column D
1234 prod1 1546 prod01
2456 prod2 1556 prod02
2456 prod2 1559 prod02b
2456 prod2 1561 prod02c