they have made reference to it (and shown it at times) previously in all three series

Yes, including the first ep which this one referenced.

in Sherlock it's more recreational use than addiction and accordingly gets casual mention

Because, honestly, from inside the show, it was ridiculously abrupt to just be like "Oh and by the way here's a list of the many drugs I just took even though it's never been an issue before kthxbai."

One thing addicts are really really good at is lying about how many / how often drugs they take. I actually found this ep powerfully accurate in that respect, that Watson wouldn't notice until Mycroft pointed it out (because Sherlock's probably been high a lot in Watson's presence, and Watson's written it off every other time too).

I think my reaction to the special can be summed up as "Oh look, Moffett's trying to be clever again". Gary fell asleep part way through.

Dang, you guys, my memory is lousy. I really don't remember Sherlock's drug use (or references to it) from the previous seasons.

So, I guess it's much less interesting that it was included last night than I previously thought, huh?

Considering how long it's been since there's been new Sherlock, I don't know how lousy that makes your memory.

I think my reaction to the special can be summed up as "Oh look, Moffett's trying to be clever again".

Yeah, that kind of sums it up for me.

I was all for the modern-day retelling of Holmes in the beginning, but when they decided to accentuate the mental instability--and when they made Moriarty an outright lunatic--it lost my interest. I don't see this Moriarty as being able to manage an illustrious academic career. He's the Joker, not the Napoleon of Crime.

Teppy-- one of those scenes has been floating around quite a bit: [link]

My memory really is lousy. Obviously it never stood out to me, which is odd. Dang.

One thing addicts are really really good at is lying about how many / how often drugs they take. I actually found this ep powerfully accurate in that respect, that Watson wouldn't notice until Mycroft pointed it out (because Sherlock's probably been high a lot in Watson's presence, and Watson's written it off every other time too).

I thought it really telling that Mary Watson had not realized Sherlock was high. The implication is that Sherlock is in fact using, while skillfully maintaining, almost all the time.

Dang, you guys, my memory is lousy. I really don't remember Sherlock's drug use (or references to it) from the previous seasons.

To be fair, I was in the fandom from 2010-2014 (I managed to write a whopping one finished story towards the end of my run in it, but it was my primary fandom until CA:TWS ate my brain), and therefore went with multiple rewatches of available material, which I still have basically memorized for S1 and S2. (I had a LOT of drawerfic. Some of which was ABSOLUTELY about drug use. Cass could confirm. I tended to text it to her.)

Whereas I've only seen each episode once, and with so much time between seasons, things fall out of the holes in my brain.