As far as I know, there are 64 Neutral and 28 class legendary cards that can be obtained from packs and/or crafted. I played Hearthstone for a couple of months when it 1st came out, then again for 3 months in late 2015. I just returned this month and finished out my collection of legendary cards.
I even got an achievement for collecting the entire classic set today.
The way I determined this was searching for legendary in my collection, then clicking on crafting. The legendary cards I didn’t have were grayed out. Now there are no legendary cards grayed out!
I was missing 5 of them today and I decided to open 40 packs to see if I could get 1-2 of them and use the dust to craft whatever was left. I didn’t get any of the ones I needed but I did get 5 duplicate legendary cards and all the rest were dupes too. I disenchanted all of those and all the gold cards and had enough dust to craft the last 5 cards. Oh, I got 2 legendary cards in one of the packs. Nice!
There are a ton of them that aren’t very good anymore, but I have them!
One more item off my Hearthstone Bucket List. The only problem is there are going to be a dozen new ones added in a few weeks.
I also crossed off reaching level 60 on shaman and I am 80 wins from gold on shaman now.