It depends on what you want to do.
Usually traders keep their continuous back adjusted data separate for testing purposes, from their trading data. In NinjaTrader for example, one strategy may be to keep the continuous back-adjusted data supplied from Portara as 6B ##-##, in the case of the British Pound. They may have their real-time trading data as 6B 12-13. However, you can merge and blend and create your own data streams based upon your own thoughts and perceptions when strategy testing.
You could have Portara set to 6B 12-13 and include the whole continuous back-adjusted data in this symbol. This way you could attach subsequent data from your real-time vendor in future months and years.
Each real-time vendor will have its own rules for callback. you will have to follow their instructions. Usually it will automatically knit into your current locally stored data. So if the data you just installed from Portara if setup as 6B 12-13 as an example the data requests from the real-time vendor may write onto that data (if thats what you want), but would skip data setup as 6B ##-## (unless real-time vendors append to continuous contracts). It is up to you to find out and do your own research.
Remember Portara Data is continuous back-adjusted data made to your specific requirements. It is up to you how you knit in any subsequent real time supplier data to this.