Hi, mueschel! 
According to https://wiki.openstreetmap.org/wiki/NaPTAN/Tag_mappings, naptan:NatpanCode=* is equivalent to ref=*. I think that generic tags (ref=*) are preferred over project specific ones (naptan:NatpanCode).  Although there is no equivalent for naptan:AtcoCode=*, ref:*=* tags are commonly used for reference numbers or codes.
Regards, Something B. 