If check in is open for your flight from IAD, there is a small chance that they will take the certs and issue your BP's. Whatever happens, they will not just take the certs and be able to authorize you to get your BP's from OLCI.

It should only be a matter of semantics though--if you have enough time at IAD, then you can still make seat changes/standby etc through OLCI, you just need your BP's printed by an agent once you hand over the paper certs.