It should work the same for a sub summary layout part, but the fact that a Sub Summary layout part represents a group of records instead of a single record means that it may be referencing data differently than you expected. and since your expression appears to refer to the table occurrence of a related table, that relationship can also be why your are not getting the results you expected.
I thought I had that figured out because the portal relationships are joined by the patient ID and a global date of service to the date of service, so the portal displays the most recent date and only for that patient. Oh well.
With this in mind is there way to get this done? Is there some other step to add to the formula calculation? I don't know what else to try.
Hold that thought! I duplicated the portal (just because of where I have these placed on the page) and put the labels inside. Works like a charm!
Thanks, Phil. You always manage to get me thinking!