I think this confirms?
"The RCIU is required along with analog loop start lines (RCOU) to provide the caller id feature. RCIS subassembly unit can be installed can be installed on the RCIU to provide 4 additional caller id circuits. "

Since we have an "RCOU3A" we'd need to install the RCIU2A to get us caller ID on one line and then the RCIS1A for a total of 4 lines of caller ID?

Please let me know if I'm getting the wrong idea.

Thanks!