Just to be precise; its' only the number of block erase operations performed on a single block that affects it's reliability, so if a single sector is rewritten too many times then the whole block (multiple sectors) is usually worn out too. These values aren't available to read in routeros.
Flash memory isn't just flash memory. There are many different types and some come with logic that helps to reduce the total erase cycles per block. Some factors that greatly impact on your typical flash drives are;
wear leveling technologies greatly extending it's expected life (Typically SSD's and some rare IDE DOM's),
bad sector remapping (most IDE DOM's and most, if not all, CF's).
singlelevel cells (great lifetime, more silicone, usually somewhere around one million writes per block ),
multilevel cells (poor lifetime, less silicone, usually somewhere around hundred thousand writes per block or less, some as little as ten thousand)
So don't expect much from flash memory that have very small form factors.
The smallest kinds have no logic other than addressing which means no wear leveling or bad sector remapping.
Move along. Nothing to see here.