Design choice random input events but sequenced output events

Problem Desc I have a situation where I am going to receive some records asynchronously from a 3rd party database (push from db), say party A. Once the data set is complete(set is complete based on condition evaluated on each record received), I am transforming the data set into set of records(json's) which are understood by another 3rd party system, say party B. Each record received from party A is transformed to a known set of records for party B.

Now, the problem is party B accepts the json's to be in specific order for the data set received from party A.

Question 1. What kind of design patterns should I use for sequencing the events for party B? I would not want to write specific implementations for sequencing each sort of data set from party A