[Yaffs] porting YAFFS, first block must be free

Hello Everyone,

I am reading "Porting Guide".

It says:
"...
int startBlock

The block number (not the address in bytes) on the chip of the first block
of this logical yaffs_Device. Beware, yaffs needs the first block to be
free so you should not set this to 0, if it is then yaffs will add on one
to it itself and also add on one to the end block which could be an issue
if you wanted your device to start at block 0 and finish at the last block
which might mean yaffs trying to write to a non-existent block.
..."

I plan to locate YAFFS above some existing data on external SPI NOR flash.
Basically, the first block is already occupied.

Can I locate YAFFS arbitrary on a flash? (i.e. startBlock=0x80)

Thanks.
Oleg