However, there are also numerous cases where the number IX doesn't make sense as 11. For example, in the possible crib for forty days and forty nights, we have IX before the number forty, which led me to suggest that IX might stand for a preposition.
As I was hunting for saints' names, I noticed the caption for the picture on page 89:
Caption from page 89: HK CUTB1C A CO D IX H HH
In this caption, I have already suggested CUTB1C = Christ, and A CO D is apparently a saint based on the common occurrence of RT A CO D. That leaves the sequence of IX H HH, of which H HH is a sequence that commonly occurs independent of IX.
To me, the placement of CUTB1C over the head of Christ (identified by the striped turban) and A CO D and H HH over the other two heads suggests that the latter are the names of the other two people in the picture.
In that case, reading IX as "and" could make some sense, both here and in "40 days and 40 nights".
That leaves HK, which could be a transitive verb for which Christ is the subject and the other two people are the object, indicating a VSO word order. The verb could be something like "appears to", giving a caption like Christ appears to X and Y.
We have HK also in the following caption on page 127:
Caption from page 127: HK QX XD CQ B1CU // RT CO C IX C ADD
The picture shows an angel making generally the same gesture as the Christ from page 89, but this time towards a figure on a bed. The caption begins with HK and ends with the name of a saint, CO C IX C ADD, who is presumably the figure on the bed.
Looking at the Latin and Greek texts of Matthew 2:19, where the angel of the Lord appears to Saint Joseph, suggests another possible reading for HK as "behold":
Latin: ecce apparuit angelus Domini in somnis Ioseph
Greek: ιδου αγγελος κυριου κατ οναρ φαινεται τω ιωσηφ
English: Behold, the angel of the Lord appeared to Joseph in a dream
The name of the saint contains IX, but it is not clear whether this is morphemic or phonemic. Certainly RT CO C never appears without IX C ADD, and certainly only one individual is depicted on the bed, so presumably IX is part of the saint's name.
If we knew the name of the saint, we might get the name of the angel, and thereby get a crib. Delia Huegel notes of this image that, if we knew the text, we might get the name of the angel and the figure on the bed. Therein lies the trick.