I don't this question has anything to do with
Exchange Web Service[
^].
What you need to realize is that EWS is nothing more than an API which helps you to implement certain functionality in Exchange Server.
And adding on top of that what you expect is not even part of a Exchange Server but definitions in the RFI for email messages.
Every email message sent (be it a first one, reply or a forward) is considered as a new mail message. It's just the Mail Servers such as Exchange Server which enable to have a trace and trail of the messages to treat them as a reply/forward.
Another factor is the email client which you are using to reply/forward the message. Even if there was(or is) any support for the headers which can define what you are expecting, it needs to be implemented by all the email clients to understand what has been requested.