It would be great to have field which can be unique (not auto numbering). That would ensure no new entry with same details is added. For each row first thing that needs to be placed can be unique field itself.
Yep, this would be a much-welcomed feature that most (if not all) other database programs already have. You may want to email email@example.com to request this feature.
You could also use a variety of methods to tag duplicate records AFTER they have already been added into your system. For example, Airtable’s Automations now lets you search fields by values, so you could search for a specified value and mark the found records as duplicates. Or you could use Airtable’s DeDupe app to manually cleanup duplicates after the fact.