In October 2012, the Reserve Bank announced that it would be introducing new criteria for the acceptance of residential mortgage-backed securities in repurchase transactions. The announcement reflected the RBA's desire to receive more comprehensive and standardised information on RMBS and to promote broader transparency in the securitisation market.The RBA has since completed a consultation process, and the new eligibility criteria will become effective on December 31, 2014. From this time on, the required information must be lodged with the bank, validated and then made publicly available.The RBA has yet to publish detailed guidance on its validation standards, which is a shame because the standards could provide some insight into the unusual RMBS arrears data released by Standard & Poor's yesterday.S&P released its arrears statistics for both prime and sub-prime RMBS for March. And, as has become standard practice, the prime RMBS arrears data includes arrears on internal securitisations undertaken for the purpose of entering into repo transactions with the RBA. Prime RMBS outstandings including internal securitisations totalled A$111.3 billion at the end of March. Excluding internal securitisations, the total is $73.8 billion.Arrears greater than 30 days in the larger pool increased to 1.42 per cent of outstanding RMBS, from 1.39 per cent, at the end of February. However, arrears greater than 30 days in the smaller pool actually fell to 1.61 per cent of outstandings, from 1.62 per cent.Thus, the increase in arrears in the month of March observed in the larger pool has come from the internal securitisations - the assets that are meant to be of sufficiently high quality to be acceptable to the RBA for repo transactions. The change in the arrears ratios referred to above does not tell the full story, however. Sometimes it is necessary to look at the raw data to see what is really going on.The arrears in the smaller pool actually increased over the month of March, by $12 million, but the arrears in the larger portfolio increased by $49 million. Thus, $37 million of increased arrears came from internal securitisation portfolios.Working back through the numbers again shows that arrears greater than 30 days in internal securitisation portfolios had increased to 1.03 per cent of outstandings by the end of March, from 0.95 per cent at the end of February. This is an eight basis point increase in arrears in just one month.  Strangely enough, while arrears were increasing among such high quality mortgages, sub-prime RMBS arrears greater than 30 days fell, on a proportional basis, and were relatively flat in terms of dollar value.Does this latest arrears data from S&P tell us that changing economic conditions are beginning to felt among white collar employees rather than the self-employed?