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If they're 6 years 6 months then you're best off not paying them. They can only stay on for a max of 7.5 years & even if you had to wait the max 1 year, it's not that long. But you can try getting them deleted already by asking the credit report agencies to delete early.
As long as they do not try to change the drop off date, or DoFD, yes they can 'update' the information.
Your TU full file will show the estimated drop off date. If you have not done so, get it at annualcreditreport.com - that will show whats going on.
I have a feeling that since your are PFD'ing them, they are simply updating in order to put the maximum hurt on your score in order to get you to cave. If its out of SOL, then CALL THEIR BLUFF. Tell them flat out, they can't do any more damage than they are already doing and if they want ANYTHING then a PFD agreement will get them what they want, which is your money nothing else.
Don't be concerned with what they try to add on - offer exactly what you are willing to pay and make it clear you will not budge. Make it clear you are willing to wait them out if they will not accept your reasonable offer.
In fact I would tell them that every week they refuse a reasonable offer your price drops 10 bucks. Make those jack###'es sweat for a change.