ACS 5 year data IPUMS Class of worker variable 0 value allocation

I am currently working with the ACS data series. We are working on a project to match an estimation methodology that uses the IPUMS data using the ACS data files directly from the Census site. 

We have noticed that the 5 year file from IPUM is significantly different compared to the files located from the Census website in terms of the class of worker variable (COW)   in the Census ACS data dictionary for 5 year data there is a 0 category which represents-“.N/A (less than 16 years old/NILF who last worked more than 5 years ago or never worked)”.  

However, the IPUM doesn’t have this category and my team suspects that IPUM allocates these 0 category class of worker observations to other classes. 

Would someone be able to share with me the IPUM procedure of allocating the 0 category class of worker observations to other classes?

Thank you,

Mike