It stands to reason that number values written sideways are recognized as such regardless if the solar disc is present or not.
Projecting your 21st century AD mindeset onto the pyramid builders is probably not the best approach here. If you are so certain that what you say is correct then you will undoubtedly be able to point to examples of the cardinal 'n' (i.e. non dates) being written sideways elsewhere. Gardiner states it is only written sideways when used as a date. This is confirmed with Moeller's and Goedicke's paleographic record.
But you seem to know better than those guys, right?