Unnecessary change. In Poland and Wroclaw using check_date is a lot more popular than survey:date and it makes it easy to see the check_date at the top of the tag list. The original tag adder also wanted to highlight having surveyed information opposed to checking it online. Tags such as note or check_date shouldn't matter if they're deprecated or supposedly used more commonly. Here locally I don't think there's a single usage of survey:date and using something like check_date:survey is perfectly fine and it even makes verifying stuff easier.