Can multiple writes to the same byte be performed without erase? Of course individual bits can only be set from 1 to 0. Unchanged bytes would be written as FFh in the buffer.
I think documentation from the 8Mbit part several years back did specify this. The current documentation doesn't 'specify' any endurance parameters except in the informative highlights section on page 1. This is quite unusual for a flash memory datasheet.
With NOR flash, you can change 1 bit to 0 using a rewrite (as you mentioned) but not the other way around. For this reason to return bits to 1 you must use erase operation first. Main Memory Byte/Page…