If the left files are hanging on the hosting in the form of the previous CMS site. Do they need to be closed from indexing?

Question

Search Engine Optimization

After updating the site, the old site was not deleted. As a result, the site on one CMS, the old site on another CMS. In the browser, you can reach both. But in general, there are no internal links to the old site from the new site. The domain what was such and remained.
If you manually drive in some of the directories and pages of the old site, then you can get to them.

Answer 1

Всё "левое" желательно или удалять или закрывать от индексации. Особенного вреда может и не быть, но старые данные могут остаться в ПС, а зачем вам лишняя старая информация в индексе...