BobKamman
Level 15

I would do the last three years, then decide whether IRS would really want another three before that.  This is how the Manual states "it depends" :

Delinquent Return Enforcement

  1. The extent to which enforcement of delinquency procedures will be undertaken will depend upon the facts of each case. As a general rule, enforcement should not extend beyond six prior years. But enforcement for shorter or longer periods, or not at all, may be determined where such action appears to be in the best interest of the Government from the standpoint of reasonableness, salutary effect on compliance, and prudent deployment of resources. (See IRM 1.2.1.6.18, Policy Statement 5-133.)

  2. Specific factors that should be taken into account include:

    1. Degree of flagrancy

    2. Special need to enforce compliance in a specific area

    3. Whether the delinquency involves trust fund monies collected but not paid over

    4. Special circumstances peculiar to a specific taxpayer, class, industry or type of tax

    5. Expenditure of resources required in relation to anticipated results in terms of revenue, provided there are no other overriding considerations

    6. Period of enforcement used by other IRS activities in return-compliance programs in the same tax area

     

  3. Delinquency procedures will generally be enforced if a taxpayer has failed to file a one-time return. In other cases when contact is made with a delinquent taxpayer, delinquency procedures should ordinarily be followed through for at least one period. However, the circumstances of each individual case must be taken into consideration. (Refusal-to-file cases referred to Examination or TE/GE after taxpayer contact has been made by examiners are required to be fully documented prior to such referral.)

  4. If it is determined that enforcement should extend beyond a six-year period, the examiner will document the case file by outlining the facts of the case and the reasons why enforcement for the longer period is recommended. Such recommendations must receive managerial approval prior to enforcement.

  5. If it is determined that delinquency procedures need not be enforced for the full period of the delinquency if less than six years, the case file must fully document justification for the shorter period. Such determination must receive managerial approval prior to enforcement except in cases where there would be no net tax due for the years for which delinquency procedures are not to be enforced.