The repertoire of Theseus 

FreeRepublic wrote on 01/17/24 at 15:18:19:

An historical bit: in his Sozin book from the beginning of the century, Mikhail Golubev wrote, "Black does not encounter great problems in the variation 6...Qb6, but he has plenty of small ones and it is high time White learned how to turn them to good account. I believe that the quite favourable statistics for Black in the Benko Variation are due to the fact that 'White' Sozin players pay, as a rule, much more (if not all!) of their attention to more fascinating variations with ...e6, and in practical 6...Qb6 games Black is often better prepared."

I notice that the ECO from 20 years later didn't appear to show a path to advantage against 6...Qb6. (Nor against 6...Bd7, by the way. I think the late IM Danny Kopec called that the Pseudo-Dragon, but there are also non-dragonish possibilities.)

Is it theory, you, or fashion that has changed most? A lot of the changes cited seem due to fashion. OK, the Marshall can kill the game now at high levels, but do you think your opponent will really know it well enough to do that? If you're not playing correspondence and mostly playing OTB in Swiss tournaments with brief preparation times, the Winawer French as Black is just as good as it was. It's still sharp, but so what? Your opponent won't have memorized a GM Rep book either, and you'll face the full-blown Poisoned Pawn more rarely than before, probably for the same reason of fashion!

I have changed my repertoire over the years, but I've done so mostly within the same openings to limit the need for studying early deviations. As Black I used to play 1.e4 e6 2.d4 d5 3.Nd2 Nf6, but now I play 3...c5 4.exd5 exd5!?. However, the KIA and Exchange, not to mention the Wing Gambit, 2.b3, etc., did not change much.

Still, the changes can be extremely disorienting after a break. As Black we face so many more White fianchetto lines than in previous decades!

Interesting posts!
1) re Laramonet: Did the same as you, playing tournaments till Covid but now half-retired & train pupils. I played 1.e4 but had to look into 1.d4, 1.c4 and even 1.b3. What works well is the Selecki KISS 1.d4 (mostly following Nf3/g3/Bg2/0-0, with some tweaks like an early g3 against ...e6 or ...f5, leading to += or workable =) and the e3-poison (Nf3, e3, c4 in some order). 
2) re FreeRepublic: with Black my main e4 answer is the Taimanov Sicilian, but after 1.e4 c5 2.Nf3 e6 I really don't like the c3 and g3 systems, while the main lines are more or less OK with some tweaking (e.g. Classical Scheveningen against Be2/Be3 instead of the risky Bb4). To thwart that, I diversified in several ways against 1.e4:
1) 1...e5 against stronger players and 1..g6 against lesser.
- For 1...g6 I used Dan Fernandez inspiratonal book (set of lines rather than repertoire), but couldn't resolve to play it  in long games. It's almost as if Black wants to feel the wind of defeat against any opponent, looking for adrenalin rather than points.
- for 1...e5 I used several sources, mostly Ntirlis, Bologan, but also Lokander which has nice ideas. I also needed to dwelve into 1...e5 as Black for my pupîls. Was afraid of massive theory (including King's Gambit etc) but now I feel there's more critical theory (what you need to know in order to survive the opening) in the Najdorf or Dragon Sicilian than in the whole 1.e4 e5 for Black. For the Spanish, I followed Ntirlis with the Breyer but never managed to get one on board, pure waste of time, YMMV. I feel Black has to be serious and learn a show-stopper (either Marshall or Berlin), plus the antis or (in my case) play a quick deviation like the Deferred Steinitz (a6 and d6) or quick g6 or Ne7 systems. They are very workable, I'm glad noone asked me to look into the Open Spanish, looks quite complex   Also, the Schallopp (1.e4 e5 2.f4 exf4 3.Nf3 Nf6) and Nf6 Vienna (1.e4 e5 2.Nc3 Nf6) are very ambitious (esp. The Schallopp with extensive analysis on Wahls site) but can be quite complex, there are more practical systems like the Ne7 KG (threatening quick ...d5) and the ...Nc6 Vienna. The 2Knights Italian (1.e4 e5 Nf3 Nc6 Bc4 Nf6) is quite interesting for Black (including Ng5 lines), but in 99% games Whites don't bother and follow up with d3/c3.
2) finally, for my own needs I completed the Taimanov Sicilian with the Classical Sicilian: afaik no forcing draws, no dangerous antis, less critical lines than Nadjorf (it's a tradeoff: 1 super critical line that splits in 4-5 systems versus more critical lines in the Najdorf), both players must be very careful, at least it works well for me. I don't know well Bc4 Qb6 for Black and I have a question regarding your statement that Bc4 Qb6 should be preferred to Bc4 e6: to me after solid moves like Bc4 Qb6 Nb3, Black always ends up regrouping with a6, e6, Qc7 in some order (my source is the Cheparinov course on modern chess + Shankland short & sweet). So, is the whole idea of Bc4 Qb6 to force/induce Nb3 before playing Qc7, and does Black win something in the bargain?
Cutting short a long post,
K.   

Changing opening theory occurs piecemeal but the accumulated changes may be sweeping. You may no longer recognize your favorite opening. Here are some examples.

Winawer French and 3...Nf6 against the Tarrash. This combination was very popular. Today, one might find the Winawer too sharp and, against the Tarrasch, prefer 3...c5 4exd5 Qxd5. The French now seems to be a different opening.

In the Classical Sicilian, 6Bg5 e6 7Qd2 Be7 (rapid development) was popular. While I still think it is still possible, I now think it leads to too many critical positions. Instead, 6Bg5 e6 7Qd2 a6 should be preferred. It's the same story with 6Bc4 e6, now 6Bc4 Qb6. Earlier 1e5 c5 2Nf3 Nc6 3Bb5 should probably be replaced by 1e4 c5 2Nf3 d6 3Bb5ch Nd7. It's now a different opening.

In the King's Indian Defense a player might have chosen the Mar Del Plata, 6...Nc6 against the Saemish, and the Panno (or ...Nbd7) against the fianchetto. I think these are still possible. However, for various reasons, a player might now choose to play differently in each case.

Changing times may have affected your White repertoire also. At one time one might have played the Ruy Lopez automatically, anticipating closed lines. Today, the Marshall and the Berlin may have you avoiding the Ruy Lopez entirely.

What to do if you looked forward to entering Sicilian main lines, but now avoid them?

The changing chess landscape does highlight the richness of the game. Yet it can also leave your head spinning.