I don't think a reduction to 23M VIA has taken place. This is what Drak wrote some weeks ago.
well subsidy was changed to subsidy halving with latest release
Viacoin Core 0.10.8
btcdrak released this Sep 1, 2015
0.10.8 Change log
Wallet:
* 824c011 fix boost::get usage with boost 1.58
Miscellaneous:
* da65606 Avoid crash on start in TestBlockValidity with gen=1.
* 424ae66 don't imbue boost::filesystem::path with locale "C" on windows (fixes #6078)
* 220ebb5 Hard fork introduces subsidy halving every 657000 blocks starting from block 1971001
you can see the changes in source code here:
https://github.com/viacoin/viacoin/commit/220ebb5d157fcee8c02f746db0545d8813f69c3f