Quick LOR question for ED apps

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I'm waiting on one letter of recommendation to show up in CAS for my application to UT. The ED deadline for UT is today. This letter has particular significance for UT and I would be completely remiss if I didn't include it in my application. That said, UT does not require LORs. So here's my question: if I submit my application today, can I add my LOR at a later date (i.e., as soon as it's available)?