Are there datasheets for this dataflash memory

It's not clear what you are really asking, but it is common to store binary values that are wider than the addressable unit of memory. For example, if you want to store 16 bit words in a byte-addressed memory, then you use two bytes. That also means the software has to know which byte is stored first.

In your case you seem to have native 4 bit words. To store a 16 bit value, use 4 words. Again, your software will have to know what convention you are using, like low word first or high word first.

Since your memory only has 4 address lines, its size is limited to 16 native words. Your native word size appears to be 4 bits, so your memory can hold only 64 bits. That means it will be completely used up by two 32 bit values or four 16 bit values, for example.

I presume your test unit uses a different physical chip. There is a huge variability of erase times possible from chip-to-chip and with supply voltage, and different ways of writing/erasing. I also presume you're not writing a file system, because that has a different set of challenges.

But the simplest thing.. are you checking the busy flag before reading the sentinel location? If the chip is in the middle of a page erase it could go off the radar for many (like 35) milliseconds.