Your post says the following.
Block Reward 15 GBX decreasing by 12% every year
In the source code it shows the deflation as...
// yearly decline of production by 12% per year, projected 136m coins max by year 2050+.
for (int i = consensusParams.nSubsidyHalvingInterval; i <= nPrevHeight; i += consensusParams.nSubsidyHalvingInterval) {
nSubsidy -= nSubsidy/12;
}
Please correct me if I['m wrong but the above will reduce the subsidy by a 12th of the total subsidy but not by 12% as stated.
For example...
100 / 12 = 8.33 which is a 12th of 100 and not 12% of 100 which would be 12 and not 8.33.
For your subsidy after the first year it works out as...
15 / 12 = 1.25 so subsidy after first year will be 15 - 1.25 = 13.75 coins
To reduce by 12% it should be...
15 * 0.12 = 1.8 so the subsidy according to your info should be 15 - 1.8 = 13.2 coins