Guardian Legend was originally an UNROM game.
Used rather wasteful code that did like:
PHAand repeat for the other six values.
where $FFF0 was a table of 0x80, 0x81, etc.
Pretty sure there was no use for the high bit on the page number in UxROM.
The only thing I can possibly think of is if maybe at some point they intended for MMC1.
I know the Famicom version was one an IREM-printed cart but it seems to also be UxROM as well.