I recommend that you upload a sample workbook.
Create two similar data sources (just make them excel sheets for this exercise) with maybe 10 rows each to simulate your data. Anonymize the data if needed.
Follow the demo video linked here:
I attempted to extract the data into roughly 8000 records but that sample is still small for me to get an accurate representation of the issue at hand. The data I am covering is over 1000 companies collecting data since 2014.
Is code the ONLY field you are blending on? If there is a 2nd field you are blending on it may be restricting the blend.