The nominal ledger count takes several things into account:
Sales invoices
Purchase invoices
Bank account entries
Journal entries
etc. Each entry to a nominal is one entry. 3 lines in an invoice to 4000 General Sales is only 1 nominal entry, and the same concept applies with purchase invoices.
One thing to note is that the nominal count is per calendar year, not accounting year. So today, any entries created between 16th May 2016 and 15th May 2017 would be taken into account. That’s going by the date they were entered into QuickFile, not the date of the transaction itself.
I can confirm that in theory deleting data will lower your nominal ledger count. But it depends on dates and how it’s entered etc. so this will depend on your own account itself.
There’s a few guides below that you may find useful, which will also point you to a report to show when your entries were created and what nominals they’re using: