As Thornback correctly describes, the DOFD is the date of the first delinquency in the chain of delinquency, and is "reset" when an account is brought into good standing, and thereafter a new chain has a new first delinquency.
The DOFD sets, under FCRA 605(c), the begin of the exclusion period for a reported charge-off or collectionm and applies to reported collections or charge-offs.
If no CO or collection is reported in a first chain of delinquency, and the debt is brought back into good standing, if a new chain of delinquency then occurs that results in reporting of a CO or collection, that new (later) DOFD is the begin date of the exclusion period, and not the prior DOFD.
However, if a CO or collection was reported under the first chain of delinquency, the DOFD for that period still applies to the exclusion of a CO or collection that occured during that first period of delinquency.
While it is very rare for an account to remain open after a CO or collection, and thus subject to a second period of delinquency if the debt is than paid, it is theoretically possible, particularly for an installment loan..
Thus, in the very rare but possible scenario where a delinquent account that was charged-off or a collection reported under the first period of delinquency, and then remained open in good standing and was subsequently subject to a second CO or collection, there could be two relevant DOFDs, each applicable to its own separate period of delinquency.