variables available under IPUMS CPS but not original CPS?

Some variables are listed under IPUMS-CPS March, e.g.,INCLONGJ Earnings from longest job, But not in the origiinal March CPS, e.g.,

Why is this the case? Are these variables created variables? Thank you.

INCLONGJ corresponds to the variable ERN_VAL (Question 48aa) in the original March ASEC data. This question asks for the income earned from the employer for whom the respondent worked for longest during the previous year.

I hope this helps. Please let us know if there are any other IPUMS-CPS variables you are having difficulty matching to the original CPS questionnaire.