You need to understand the concept of a subfile.
If you set SFLSIZ at 9999 and filled it before you did the EXFMT, you would have done I/O for 9999 records, plus any other CHAINS that may have been done.
If the SFLPAG was 20, what user would page through 500 pages to view data? You wasted a lot of resources.
You can read and display the 20 records, then when user uses a page key, you get the next 20. Now you have 40 records in your subfile. so you can page backwards without doing database I/O.
When the user does a refresh of the subfile, you start all over.
If you really have a need to page through more that 9999 records, reset the subfile with every page key and the cod for forward and backward processing.
As long as the question is about a “LoadAll subfile”, the answer will always be “You can’t.”
In other words, if you want to display more than 9999 entries, don’t use a “LoadAll subfile”. Use a page-at-a-time subfile instead. There is no point in trying to cram 10000 rows into a structure that only allows 9999 when only a single screen is ever going to be shown at a time anyway.