The merge command in DEVONthink actually orders the documents based on the sort order of the group containing the documents. I addressed that in an earlier post on the forum located here.
The relevant (to this discussion) summary of that post is this:
“What does determine the order is how the documents are ordered in the list e.g. if you sort alpha ascending, then the documents will merge docA, docB, docC,… Sort alpha descending and the documents will merge docC, docB, docA,…”
If your merged documents are ordered with the number highest to lowest, it is likely because you have the group sorted in Descending order. Change the sort order to Ascending, and you should see the results that you are looking for.