I guess we should not kill the messenger who deliver the bad news. Yes, the biggest mistake here is DBS inform the customer almost 3 months late. But who discover this error (DBS or MAS) and DBS being his SRS operator has to inform the customer and offer a $50 gift as apology.
If the online application is what we think it is (all the e applications with DBS, UOB, OCBC are uploaded to the aggregator MAS electronically without massage), and MAS is the one who is in charge of the allocation, then perhaps it is MAS error and not DBS error.
CPF Tbills application via paper application is a different story as there is a certain amount of text (from paper application form) to data conversion done some point in time before it is being aggregated with the online applications.