It appears that when loading data from a universal forwarder when the data is header structured (e.g. CSV, TSV), one must edit props.conf on the forwarder in order to tell splunk that the sourcetype has to be handled differently.
Example is:
[backtestMetaData]
INDEXED_EXTRACTIONS = csv
NO_BINARY_CHECK = 1
However, the settings will be slightly different from the props.conf on the indexer, which may need to apply custom timestamp rules.
I found this document to be a a very useful explanation of the process;
https://wiki.splunk.com/Community:HowIndexingWorks
This question was also useful:
http://answers.splunk.com/answers/153488/does-a-universal-forwarder-ever-read-props-conf.html
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