No, there was literally a public Google form: https://docs.google.com/forms/d/e/1FAIpQLScndnMojIJoflfSPTD2...

They later moved to a self-hosted form, which remains available to anyone who wants to report a purported casualty: https://sehatty.ps/moh-registration/public/add-order

This has been well known since early last year, when Hamas themselves spoke about their incorporation of these other sources.

Casualty reports slowed down presumably because the fighting slowed down; in any case it's not a reason to make assumptions about Hamas' methodology that are contradicted by easily verifiable facts.