I was thinking using ZWJ because the staff is always implied by the usage of Cistercian numerals. I was also wondering if we could reuse CISTERCIAN 1-9 for each significant digit rather than having to encode all 4 separately, though at the end of the day it’s only 36 separate code points.

Adding the staff is 37 codepoints versus 36, but I think using ZWJ would at least have each numeral independently renderable so it degrades gracefully. I’m not too sure about how combining characters degrade.

Essentially it boils down to whether you think the staff and the digit flag part of the numeral are independent or not.