Nope, CGS is a modern concept, you cannot retroactively penalize Sampras for not wining the French open.
Before the era of homogenization nobody used terms like CGS in the media, show me any article of Agassi's CGS being mentioned as a term in 1999. You cannot because back in the 1990s wimbledon itself was a more prestigious slam than other 3. US open itself was more prestigious than a French or AO ... the AO was the least prestigious. Boris Becker with 6 slams only was a bigger name worldwide than Lendl because of 3 wimbledons that are greater than 3 french opens... the way the world looked at tennis was different pre homog and post homog, you are mixing the 2. Nobody considered Agassi even better than Becker in the early 2000s because Becker's wimbledons were a big deal even then, later on CGS term was coined in the post 02 era.
Nobody cared if Borg couldn't CGS. Borg only won 2 slams out of 4 but he is respected for 5 Wimbledon alone and 6 Frenchs. Those 5 straight WImbledons alone kept his name shining in the media. That era was judged on Slams prestige along with ATP Finals & davis cups, not on CGS..... Penalizing Sampras for his lack of french was all started by Roger Federer fans itself. It is cruel karma for Roger that he lived and had to die by his own sword, what was marketed as CGS became DCGS later on and now TCGS, in future it will even become QCGS. Then what? Will you penalize Sampras for not winning all 4 slams at least 3-4 times?
Sampras was exceptional on fast courts, so not winning all 4 slams is a price to pay for him, even Federer has not been that exceptional on fast courts because courts have never been that fast since 02, so why would Fed's CGS hold that much weightage now? Absolutely not. 14 Slams are 14 Slams only. Federer was actually rated ahead of Sampras long before he reached 14, but that doesnt mean the official consensus ws obtained on 14, that only happened on 15, thats why the legends were all there to click pics with him.
Try winning 3AO, 2FO, 2W and 2USO, you will be rated below Borg with 5W & 6FO .....the big numbers are more eye catching ... the whole world speaks of Nadal's 14 french opens... because it is the greatest feat in Tennis .... to overshadow that you need a higher slam count.... as simple as that.