Trying to understand the FLASH region of an STM32L433
You're completely misinterpreting page 78 of the reference manual.
Firstly, that document applies to more than just your 256kB STM32L433 - it also applies to 128kB and 512kB devices in the same family.
Secondly, Table 8 does not list every identical page of 2k flash. There is flash between pages 3 and 63, and between 63 and 127, and between 127 and 255 (depending on if the specific device in the family has that much flash). Listing them all would simply be a waste of space.
You'll also notice that the lines for 63, 127 &amp; 255 each have a superscript number which refers to the notes immediately underneath the table telling you that these are the end pages for each device variant.
The datasheet for your specific STM32L433 part is correct and unambiguous in stating that it has 256kB of flash.
The reference manual for the family of which your STM32L433 is just one member does not contradict the datasheet.