Sometimes, there is one grapheme for multiple meanings.
‘scheppen’ can mean ’ to create’ as well as ‘to dig’. In Dutch, both forms of ‘scheppen’ have different derivatives:
scheppen, schiep geschapen (create)
scheppen, schep, geschept (dig)
To be able to refer to just one of the verbs, more is needed than the grapheme of the root and its word type. Some part would be needed to identify the right meaning. In dictionaries, this is often just a number.
Technically, it would be possible to add it to the postag, But that would have quite some impact too. Would it not be more ‘pure’ to have it as an extra field?