In Svami Desikan’s Prabandhasaaram, in the pasuram “vaiyagamoN poigai bhUtam pEyAzhvAr..”, after mentioning the 12 Azhvars, he has included the name of Yatiraja “iyyan aruL kaliyan yatirAsar tammODu..” towards the end. But Iramanusa Nuttrandadhi was compoased by Tiruvarangathamudanar. Why did Svami Desikan exclude Amudanar’s name and include Yatirajar’s name?

Tirukkurugaippiran Pillan was the first to include Ramanujar in the Azhvars’ group.
bhUtaM sarashca mahadAhvaya bhaTTanAtha
shrIbhaktisAra kulashEkhara yOgivAhAn |
bhaktAngrirENu parakAla yatIndra mishrAn
shrimat parAnkushamuniM praNatOsmi nityam ||
Our tradition follows the path shown by Pillan. Hence Svami Desikan also included Ramanujar in the Azhvars’ group. Pillan’s sampradayam includes Iramanusa Nuttrandadhi among the 4000 Divya Prabandham. This was established by Pillan. Those traditions that do not follow Pillan sampradayam, do not include Iramanusa Nuttrandadhi among 4000 Divya Prabandham. Hence in our tradition, we included the name Ramanuja along with the Azhvars.
In the Prabandhasaaram, while mentioning Iramanusa Nuttrandadhi, he says “kAsinimEl vAdiyarai venRu arangar gatiyAga vAzhndaruLum etirAsA! Mun bhUsurarkOn tiruvarangatthamudanAr un ponnaDimEl andadhiyAga pORRi pEsiya”, about Tiruvarangathamudanar. In the pasuram where he lists and totals the 4000 Divya Prabandham, he mentions Amudanar again.