Smart collections organised by keyword not working as expected

Hi there,

I'm not sure if this is a bug or I'm misunderstanding these functions. I manage a very large LRC library for a holiday tour company which takes images of clients during their tours. The library is currently 81748 images in size. In order to manage this, I have a large number of keywords, as well as smart collections, to organise and search for specific kinds of images. The images are all tagged with a trip code based on what tour it is from. This is made up of a three letter code such as "ABY", a letter which designates what year it is from, and a number which designates what week of the year. A full trip code looks something like ABYB22. The codes are distinct enough that theres no overlapping in terms of keywording.

I have a series of smart collections set up to collect the best images from each tour - each collection is set to gather all the images with a given tour code ("CAL") and which are 5* rated. I've attached a screenshot of the smart collection settings. My understanding is that, with the keyword setting set to "contains", the smart collection should gather all images which have a keyword starting with "CAL". However, it seems to be gathering a lot of other images to. As a representative sample, the second screenshot shows the keyword tags associated with another image which is being included in this smart collection. I'm not sure what I'm doing wrong. If I set the rule in the smart collection to "contains words", it does reduce the number of images in the smart collection, but I'm worried its missing some out, and because of the size of the library, it's not practical to check manually.

Can anyone advise on what I'm doing wrong? I've looked at they keyword tags for that example image for a good hour straight trying to see if there's just a series of CAL that I'm missing somewhere in there but I don't see what it is.