It depends on your perspective of what a classic is, does it have to be 5 mics perfect or is it a classic in the traditional sense of memorable and impactful?
I tend to look at 5 mic albums as masterpieces and there's honestly perhaps less than 15 in the genres history. But then I also think other 4 or 4.5 mic albums throughout the culture's history are classic in the traditional sense of they had really good songs. people enjoyed them, they are memorable for the time and we go back to them to appreciate eras. They are FAR more of those and I think Nas has that.
To me he made a masterpiece in Illmatic and while none of his other albums were up to that level, they didnt need to be for him to have a memorable discography. When I look at other rappers and the classic albums they have in their cataglogues its usually landmark albums that added to their storied career
In that respect I do think at least It Was Written and Stillmatic were classics as well. They were memorable and impactful for the time (An underground MC crossover while still maintaining street raps and a comeback album that put things in proper perspective)
To me It Was Written (and to a far greater extent Reasonable Doubt) grew in their classic status because the backpacker mentality softened from what people first thought of them and saw that it still had great street records and was a good snapshot of a certain of rap (QB golden age, mafioso rap). I also think it had impact, Just Blaze always cites the fact that this and Stakes is High (another album I consider classic even others dont) dropping the same day created the NY civil war of backpackers vs big willie style glossy street rap (which wasn't really settled until Blueprint united both sides)
Stillmatic, is a flawed album but so are other albums we call classic, there was still enough quality material and lyrical perspective for the streets that made it impact. Ether, One Mic, You're the Man, 2nd Childhood, Destroy and Rebuild, Poison are songs that stood out so strong I think they outweigh the negatives which honestly aren't that bad. More over, the symbolism of the album as a modern day comeback album in Hip Hop is just too strong to ignore. And even for missteps like braveheart party, the dudes overall demeanor and confidence on the album is just too strong to ignore
Also, dont forget, I think both albums earned him new generations of fans and made him more than just "The Illmatic guy" and that's gotta count for something, because if a guy is strongly considered top 5-10 and its not always his best album that people say are their favorite that's more a tribute to him having a more solid discography than people.
Because both albums had impact on the scene when they came out and are fondly remembered, those albums should definitely.
I would put God Son and Life is Good as just below classics but just below under very good/excellent albums as well. Because while I dont think they may have had a greater impact on the game at the time like Stillmatic and It Was Written did, best believe they were key chapters in Nas career. Life is Good has quietly become the blueprint for a grown man album. When people how a rapper can age gracefully and what to rap about when you hit your 40s, that album comes up a lot when critiquing other albums. God Son is probably his most personable album and for a guy who always had this perceived
Also one tier below in good but not classic are Hip Hop is Dead and Untitled which SHOULD have been impactful albums but while decent to listen were muddled by production inconsistencies through the album to really be the impact albums they should have. I dont think Untitled was so bad and neither was HHID but HHID was like an actual trending topic album and the music and theme should have been consistent which would have made it a classic. Much I Am its a blown opportunity. The rest of his stuff is kinda slept on not bad. I liked Streets Disciple for what it was but I think obviously weight and oversaturation of the double LP hurt it even though I think its got some classic Nas records on it (Theif's Theme. War, Streets Disciple, Just a a Moment etc)
I get that there's a mentality with a certain generation of fans that if you cant match your debut album, everything else you make is trash and their expectations are only a product of what you gave them... But he's had way too much of a storied and long career and even the most harshest Nas critic probably finds themselves listen to a long mix of different cuts from him to say that he doesn't have any other classic beyond Illmatic.
When people discuss rappers with great discographies, his is the most strongly discussed for if he is or isnt and doesn't it say something that even your wack shyt is memorable because where always having a discussion on the varied range of what they drop? And if more people were honest, a lot of dudes who we say do have multiple classic albums also have the same inconsistencies in their albums but because they best isnt Illmatic or the worse aint Nastradamus we dont seem to argue it out more
So to me he's definetly got 3 classics in terms landmark Hip Hop albums and a the rest of his stuff is a range of albums that go from great to average to frustrating for his standard. But even at his worse I dont think he's never had an outright doo-doo album like Encore or some of Snoop's stuff or Electric Circus or maaaaybe BP 2 (this could be debated because much like Nas I think even Jay's worse is pretty good). So I think he still has one of the best discographies in the game.
Or if you've got a more stricter perspective and think everything should be up to par with Illmatic and he's got only one good album....that's fine too but then I hope you're not saying all these other dudes who never made an album as good have got like 5 or 6 classics either. All depends on your perspective.
Bit of a ramble I know
but yeah...he's got 3 classics to me and the rest is good