Where is the January security update release of current channel?

Deferred Channel (DC) 1605 and Current Channel 1611 are about 6 months apart from a code perspective. So it could very well happen, that discovered security issues is only affect a subset of available channels. The code in other channels may already have changed and the issue was (maybe unintended) mitigated even before it was discovered. Protecting customer's security is a priority for Microsoft, rest assured that no security fix is held back when it is ready.