This sentence is placed under the section "Flow diagram (wihout an Intermediary", hence isn't the statement contradictory? Also quite some assumptions are made for which further explanation and clarfication would help.

Existing Wording:

 However, since the implementation guide explicitly calls out the use of intermediaries, keeping track of the correct MessageHeader.response.identifier value would be an additional requirement for them that is not necessary - the use of Task allows responses to be linked with the original order without MessageHeader.response.