I spent some time playing with own code and your design file and it seems there is a bug (in fact there are many bugs in VBA ItemTypes API). Not sure, but maybe it relates also to problem with names with spaces, discussed here in relation to…
Could you please check if you have mapped the Variables of the Parametric cel to the Parametric Name in the Catalog Editor?
Once the variables are mapped, the current values will be displayed during modification .
For a simple view to a the list of all the files in the current folder I use a LinkSet with the config variable $(_dgndir)*.dgn without any filter.