I agree with fused. FICO is a proprietary scoring algorithm, and details of its inner workings are, for obvious reasons, not published.
All remain, in some fashion, for up to 7 years.
All we can really go upon are anecdotal experiences.
We only have a few specific, factual statements from Fair Isaac.
FICO scoring is primarily an attempt to rate your risk of becoming delinquent within the next two years. When any projections, including those made by the Fair Isaac gurus, stretch beyond two years, they begin to enter the realm of psychic prediction rather than scientific analysis.
From my experiences, and what I have seen reported on this site over the years, this is my subjective opinion on the effect of derogs.
Everyone wants numbers, so here is my opinion.
When you first go 30-days late, the initial FICO hit seems to be around 20 points. It seems to then decay at a linear rate of appox. 1/2 point a month. This is a minor derog. After 3-4 years, it has little remaining effect.
When you first go 60-days late, the intial FICO hit seems to rise to around 30 points. This is the first of the major derogs.
60 day lates, from my experience, also seems to decay at about 1/2 point a month. But many on here have reported that after two years, the effect of 60-day lates becomes the same as a 30-day late, so at 2 years, is probably hitting you for around 14 points, then continuing to decay at approx 1/2 point a month.
When you go 90+-days late, you are in the realm of serious major derogs. Probably an intitial hit of around 40 points, and then decaying, linearly, at around 1/2 point a month, up to their termination at 7 years.
Collections, charge-offs, and public records, also being major derogs, seem to decay at about the same rate.
But, as fused has said, it becomes very complicated. Depending upon your scoring bucket (which algorithm FICO assigns you to), the weigthing of payment history can vary markedly. For example, one with a credit history of 20 years is scored, with otherwise identical derogs, different than one with only a one year credit history.
This may confuse more than help, but one thing is certain, at least to me. Any derog has substantial short-term effect, and the decay of their effect is probably less than one point a month as they age. No magic numbers.
What may have more significance in your CR when a creditor views it is the status of the derog debt. FICO, being a predictor of the likelihood of missing debt payment, does not score old derogs any differently whether paid or unpaid. A prior missed payment is still a prior derog. But a potential creditor will frown deepily on an unpaid debt. It is not all just about FICO.
My opinions only.
