A quick update for anyone interested in this!
I created a number of blank files with just headers and no data.
These files have parameters in the filename, e.g. STARTDATE, ENDDATE.
I import the filenames into a table and update the parameters based on a "setup" file which has the month required, client info etc. in it.
I then compare the list of files in a client data directory with the reworked filenames of the blank files, and filter for those only files that don't have a match.
I then copy the blank files into the client directory, and then rename the blank files in the client directory, e.g.
blank file - transaction_CLIENTMANE_STARTDATE_ENDDATE.csv
becomes - transaction_joomtree_20220101_20220131.csv
Then in my main processing file, I make sure that where there could be no data I use the Skip action where the table is empty so as to not create any errors.
Anywhere any figures from the empty table should appear where I'm appending data to another table, I'm adding in Calculate New Column actions with the column names so that any Aggregation that is calculated is still calculated if the data doesn't exist - I set the values to 0.
If the data does exist, the Calculate New Column action columns get appended with "(2)" which is then removed when the Aggregation happens!
So far this is working very nicely.
This has really highlighted how wonderfully EasyMorph surfaces errors and links directly to where the error is for you to resolve.