404s

Got a domain say abc.com

Without thinking we ran a few deployment sites under new.abc.com , old.abc.com (a few of them) - then deleted the sites and google started registering them as 404s

We did put up 410 response codes on those but google is still counting them in our search console. And on a 20 page site it racked up about 900 404s

Wondering if these have effect on SEO as since the # of 404 went up our ranking has been dropping and I am thinking there is a correlation but cannot find anything concrete when i search for it.