Caution: NEVER change survey flow while collecting data

I discovered something painfully.
I had a survey in the field. My intention was to collect X number of responses to questions in blocks 1-5. Then I would stop collecting answers to blocks 3-5 and instead collect answers to previously unshown blocks 6-10. In my situation, it was not feasible to issue a new link for the new version. Instead I changed the survey flow so that new respondents saw the new set of questions.
Turns out, when the survey flow is changed, the survey loses all the data associated with the blocks I'm no longer keeping. [To get it back, a Qualtrics tech suggested reverting to the original survey once I've finished all data collection, although she said it's not certain that first set of data were retained.]
It would have been helpful if a warning popped up: "Stop! When you change the survey flow, you're going to lose all the data you've collected. Don't do this! This means you!"
Better still, it would be helpful if Qualtrics offered the option to hold onto all the data I had originally collected.