Is it possible to get the cheapest price by date with prices for outbound and inbound separate, rather than combined?

The full price is obtained by combining quotes from OutboundDates and InboundDates listed in the Dates block. 

In some cases, the price will be the sum of 2 (or more) separate quotes, often one outbound and one inbound (listed separately in the Quotes section). This is when the 2 legs can be purchased separately (e.g. Budget airlines). An example of 2 separate outbound and inbound legs would be:

and

 

Where the outbound QuoteId is 1 and the inbound QuoteId is 9, which are listed in the Quotes block:

In other cases the combined price is a full return quote that cannot be separated into individual legs. This is the case for scheduled airlines (e.g. BA) where the price of both legs is only applicable when the return flight is purchased.

So for example in the case of a return quote the outbound and inbound dates would have the same QuoteId: 

Where Quote 3 is a full return quote: