My use case - I've found a good amount of 13zb1hQbWV prefix matches for puzzle 66 so far. When I convert their hex key into their base10 decimal number, I notice many of them (about 1/3) have a factor of 13 and/or 17. An example is 3FEE2509944801483 (13zb1hQbWVECopz4XMEYH8e2t2gX4v4Us3) = (decimal) 73706563070708421763 = 7 × 13 × 809962231546246393.
Turns out that you were right, but it's just a lucky statistical guess in my opinion.
Priv key for puzzle 66 : 0x2832ed74f2b5e35ee = 46346217550346335726 = 2 × 13 × 17 × 104855695815263203