Are you sure that form example there is 10^75 combinations, it seems like a lot

, since all BTC priv. keys - 10^77?
10
75 is 1% of 10
77.
Bitcoin private keys fall within the following range:
0000000000000000000000000000000000000000000000000000000000000001
FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364140
The two keys seoincorporation has used:
C3B7C35F28C8A6089657B848366FB2E0A48D35E36B2184EF0DFF520E217CAD3C
CB7BAEE72882261268C582EBFCFEE7E1CFBD166F8DE3FF2182A11228D9D98217
calc
C3... to CB... is around half of all keys starting with C. Keys starting with C are around 1/16th of all keys. 100/16/2 = ~3% of all keys.
So yes, the range shared above is two orders of magnitude lower than the set of all keys.