That is a great question you posted. It appears your client filed a return on 11/20/2006. There was then an additional assessment (Possibly automated underreporter or an actual audit) on 5/20/2007. Each of those actions will have their own CSED, based upon IRM 220.127.116.11.1-”Each tax assessment has a CSED. Internal Revenue Code section 6502 provides that the length of the period for collection after assessment of a tax liability is 10 years. The collection statute expiration ends the government’s right to pursue collection of a liability.”
The subsequent tax assessments are associated with an IRS internal transaction code of TC 290. The sad thing is, the 290 could represent a number of different actions (the generation of a “freeze” code that will keep any refunds from being issued, penalty abatement request that was rejected, and a host of different other reasons). The general public will be unable to know what the root cause of the TC290 is, as the IRS uses reason and source codes that are privileged.
With that being said, you and your client should focus on the two primary assessments that expire in 2018 and 2019.
Hope that helps,