I also know they do, (a) since I've well-doned one of the FT cabin crew here without telling them and they confirmed via unsolicited PM it had got to them and (b) I once well-doned a team who received my feedback so quickly that they knew about it for my return sector with the same crew. I think that speed is unusual, I gather it normally takes a few weeks, so when making the comments it is also worthwhile to add in some unusual specific that will trigger their recall of the day - e.g. weather or unusual delay or unusual passenger behaviour. I keep the form bookmarked on my mobile phone, so I can send it off before we've left the aircraft.