What?
Why would we lose all the data?
It's not me who created these issues with the spreadsheet - it's because of an update done by Google. I don't blame Google for this, as the changes they've made can be considered an improvement for particular cases, but it's still a rather aggressive spreadsheet behavior change from their side.
By the way, I wanted to tell that I've just finished fixing these issues. All 19 affected entries were successfully recovered/fixed and no data has been lost. Charts are now fixed as well.
Regarding data safety, the data is stored not only in the spreadsheet, but also separately as a list of form responses.
In addition to that, I've been backing up the spreadsheet regularly, and I've implemented automatic daily backups today.
Perhaps the only thing that could be improved here is to store those backups somewhere else, so that they can't be modified or deleted. Like on a magnetic tape ;D Otherwise, we have a fairly good backup system already.