Yes it increments the starting priv key at each step but generates also 5 other points from it (no way to disable the 5 extra points without code mods).
To start with a specific priv key, the only way is to specify the corresponding public key using -sp option and reconstruct final key using -rp option.
If specify the corresponding public key using -sp option, the tool just adds some "unknown" number to the priv key. This is very useful for work delegation.
My question was about start search from the exact priv key. You have base key in your tool, but it is not determined as the exact 256bit number to start, it is determined by the seed. How do you receive the base key from the "-s seed" option as the starting point?
for this task.
VanitySearch-1.15.2_bitcrack -stop -t 0 -gpu -r 10000 -s 0000000000000000000000000000000000000000000000000000000400000000 1PWCx5fovoEaoBowAvF5k91m2Xat9bMgwb