Credit reports are complex animals (interaction wise) and unfortunately Scorewatch is smoething of a blunt instrument as it doesn't catch a lot of subtle changes: unless something overt like a balance changes, or something new gets added to the report (inquiry, tradeline, derogatory) it doesn't pick it up... and a lot can happen unfortunately in that margin (like an existing tradeline or derogatory changing it's reporting status, which can be huge).
It's incredibly hard without looking at the full before and after report for anyone to say: yup that's it! And even with that, it requires a lot of analysis and as such I really can't make any reasonable suggestions for why you lost the points: also I'd suggest it wasn't a huge change, there will be lots of ups and downs like that through the course of your rebuilding, don't stress out over that, otherwise it'll get REALLY fustruating.
Regarding old derogatories: not every derogatory is created equally in severity, and while newer derogs are definitely higher penalty (assuming same severity / type) it looks like with my tax liens anyway that FICO was also doing an aggregate count in there: as such, reducing the number of derogatory tradelines of any age can produce non-trivial benefits to one's score. Virtually any negative information being removed is a good thing, regardless of whether it's 10 minutes or 10 years old.
