I can not make heads or tails out the codes for HUHHNUM. I think maybe the labels are missing? I don’t see any with either Firefox or Chrome.
The HUHHNUM variable is one part of the original unique ID variable that can be used to link households across the CPS samples. So, I do not think you are missing anything. The codes should only be useful for uniquely identifying households. Note that when using only IPUMS CPS data, this variable is made obsolete by the CPSID variable. We make the HUHHNUM variable available for users who are interested in linking IPUMS CPS data with NBER CPS data.