I'm thinking they aren't the sort of figures for which people would want records kept. This is the sort of thing one does in the dark so as to avoid the moral opprobrium directed at himself by his neighbors and fellow abolitionists.
Some of it could possibly be reconstructed from existing records, but I think a pretty good statistical reconstruction could simply be had by assuming most previously held slaves were sold in the South.
I attempted once to come up with some numbers from census data. Number of free blacks and slaves in the census before emancipation versus that in the next census.
Got bogged down. Not sure the method is usable. Too many unpredictable variables.
Most people don’t know that in most northern states emancipation was gradual. At least the northeastern states. The midwest states were born free. At least in theory.
If I remember correctly NJ still had a very few slaves in 1860.