This is a piece of 4th Series replacement note with the Prefix of ZB. Notice that this replacement note does not carry a 50th Anniversary logo at the upper right corner of the note. Thus, it is believed that this replacement note is designated to replace the mistake notes with the Prefix of AF and later.
4th Series of Malaysian Banknote - RM50 Replacement Note with Prefix ZB
Unlike the replacement note of ZA, the logo of 50th Anniversary is depicted at upper right corner of the reverse side. As discussed earlier, only the prefix of AA of these RM50 notes are with this 50th Anniversary logo. Hence, ZA replacement note is meant for the replacement to the note of prefix AA only? You can prove it otherwise if you can find a replacement note of ZA that is without the anniversary logo.
ZA Replcement note with 50th Anniversary logo depicted on the upper corner of the back side of the note.