Filters should not react any differently to the first compared to the one thousandth. How could it ? That said I created a few rules in MS Outlook to divert advertising (from places I've bought from but are too keen on sending more info) and whilst they work fine on some, there are a few that are unrecognised as being from the same sender each time. I'm unsure why.
Are you using an e-mail client ? If so why not install and use Mailwasher. Makes hand filtering easier.