We tend to send quite early, first week in December. We have a computer list of names (it's around 35 this year) which we print out each year and tick when we've received a card back. We keep the spreadsheet in the Christmas Card box so next year, we'll know who we've received from this year and can amend the list accordingly. Mrs O also records the Christmas presents we've given to nephews and nieces, so on, so we don't duplicate the following year (although they're all reaching the age now where it's going to be easier to send them cash!)
There are a couple of folk we sent to this year but we did not receive from; they were elderly and unfortunately we've no other way of checking what's happened to them, so regrettably we'll knock them off the list next year.
What we have done this year is keep any cards we've received where they contained messages saying that the sender has been poorly or perhaps there's been a family crisis in 2017. There were a number like that this Christmas - none of us is getting any younger
. Mrs O has written back to a few of them already; the others, we'll be able to send more personal messages next Christmas rather than the ubiquitous "Hope you're all keeping fit and well ....." It's so easy to forget over the course of the year ......