spring time everyone remembers, Nov, Oct not so much.
Not true for mine - DS has a Nov birthday, we have 2 sets of friends with similar aged DC who we exchange with. Since all 4 of their kids birthdays are Oct/Nov (with one from each family being close to DSs) they never forget, though one is consistently late, but just a day or 3 with DS.
DD on the other hand has a June birthday. They have both totally forgotten in the past. Since they dont live locally and send via post, I usually question after a few weeks, using 'Did you send something, as we want to send a thank you if you did'. One family has generally remembered since then. The other is usually 2 weeks late at least, but something arrives eventually. It is her 18th this year, I had hoped when oldest ones turned 18 (my DS and another) we would stop but both families were adamant they wanted to go on to 21!!!
My SIL 'forgot' DS birthday last year, despite her DH's being the next day. He is at uni, but was home the day before, heading back early on his birthday. Most people (he doesn't get much now!) sent cards to us in good time, so we could forward on if he wasn't home. I do same with SIL kids, or even ask for their uni address, not that hard. I did ask DH to question his sister, which he wasn't keen on but it was out of character and we wanted to know if it had got lost.
We got a 'sorry its late, in the post' message. It arrived here nearly a week late, then needed sending on. Why oh why didnt she just ask for his uni address?
I would have to say something Op, just outright ask if you are doing presents for DC in 2018, as they seem to always forget your DD. If they still don't send anything, then stop their DC. It should kickstart them to either restart your DD, or stop all your DC, both of which are better than current scenario.