EMIR requires that Non Financial Counterparties under the clearing threshold (NFC-) reconcile their portfolios of uncleared OTC trades once a year, for portfolios of 100 trades or less (quarterly otherwise). The 15th March is both the deadline set in the ESMA Q+A for the annual reconciliation, and also the day on which those under the ISDA protocol generally carry it out.

Many in the market are not fully up to speed on portfolio reconciliations, and are relying on patchworks of spreadsheets and emails. It will be interesting to see how it goes. 

Do not forget that the FCA have also set a deadline of April 30th after which they expect all under their jurisdiction to be compliant.