Technically, I dont think that a challenge of credit report exclusion is a disputable matter, as it is not a challenge of accuracy of reporting, but rather failure of the CRA to have dont its job. But that is a separate issue.
If you send a dispute, the CRA is required to complete their reinvestigation within 30 days of the date of dispute (unless additional supporting info is provided by the consumer, which extends their reinvestigation period to 45 days). They are then required to send their Notice to you within 5 days after concluding their reinvestigation.
If they considered the dispute to be improper, they have to send a notice that it is dismissed as frivolous or irrelevant. If they accept the dispute as proper, they have to send a Notice of Results of Reinvestigation. Either way, they have a statutory period running against them that has no provision for extension. if they cant verify the accuracy, they must delete until such time as they can provide verification.
How are they extending the period to either dismiss or send notice of their results? I know of no statutory provision that enables them to do so........
