You are correct that ‘-1’ represents ‘no spouse of this person present in household’ in the earlier years. The ‘-1’ values should be coded as ‘0’. This is an error in the IPUMS CPS data and will be corrected in the next data release at the end of this month.
Thanks for catching this error. We like to reward users who bring errors such as this to our attention with an IPUMS coffee mug. Please send an email to ipums@umn.edu to claim yours.