Q: Why doesn't Cortex_pgm.exe enable readout protection ?

A: After programming the STM32L151 using "O" option, the Cortex_pgm.exe DOES NOT report the CPU to be read protected, before a new erase+programming is started. It is POSSIBLE to readout the content while it works for the STM32F070.

The option byte "O" option through command line cortex_pgm.exe doesn't allow readout protection for the newest devices. In order to activate readout protection (or other option byte) you should use "OF" option (add source code option byte file to your project, configure it as you need and compile it).

Everything is explained in the getting started p36-38.