@ChubClubThug shares a lot of my sentiments.
The example I always use when criticising the writing of the 2019 special is this:
Stacey says "like over there by the bingo hall, that's where you rang me and I ran out into the rain" and Gavin said "oh yeah I think I was at a foam party at the time".
That is such a clunky and unnatural way to write it, when they could have really driven the point about Barry Island being full of their history. I'd have written it like this:
Stacey: Do you remember when I moved back home just before Neil was born? I thought I'd never see you again, I was a mess, sleeping on Uncle Bryn's sofa. But that phone call, I knew then that we were going to be okay, because I love you, baby.
Both: That's just the way it is.
Now, I'm not a professional scriptwriter, and I may be a few pints in right now, nor am I claiming this is too notch writing. What I am saying is that there are PLENTY of naturalistic ways to throw back to previous episodes/events. In that bit I've written, I've thrown back to a specific time in series 2, picked out two events that happened in that series, and made reference to what they said to each other when Gavin found out she was pregnant.