A memory apparatus and method of operation is provided. The apparatus includes a block of memory cells arranged in strings and connected to word lines overlying one another in a stack. The block is divided into first and second sub-blocks programmed as a whole in a sub-block mode and includes a particular group connected to a particular word line. A control circuit determines whether the particular group being read is in the second sub-block when operating in the sub-block mode. The control circuit also determines whether one of the first and second sub-blocks is not programmed based on whether the particular group being read is in the second sub-block. The control circuit applies an adjusted read voltage to the word lines of the one of the first and second sub-blocks while reading the particular group based on whether the one of the first and second sub-blocks is not programmed.