Daniel,
I'm not able to say if Lucile was mistaken or not in claiming the Astors and Strauses dined together in the restaurant on April 14. It's possible she confused the occasion with an earlier dinner, either in the restaurant or in the dining room. However, there's no evidence I'm aware of to suggest the Duff Gordons ate in the dining room at any time.
Lucile, like a good many other regular first-class travellers, was used to some of the German ships which had the "Ritz" restaurants aboard and she may have been spoiled to this type of more intimate dining. I must say the pictures I've seen of the dining room on Titanic show a very imposing, sprawling space, not at all warm and welcoming.
Remember, too that the Duff Gordons were travelling incognito to avoid attention, a concession the publicity-happy Lucile had made to spend more quiet time with hubby Cosmo. So it doesn't seem likely they'd have made an appearance in the main dining room where she'd have been seen by nearly everyone. Another indication that she may have opted for the a la carte restaurant in lieu of the main saloon is that I've found several references that she had a special corner in the restaurant of the Paris Ritz always reserved for her; so it makes sense that she may have repeated this preference on shipboard. We know, for instance, from Walter Lord in his article "The Maiden Voyage" (American Heritage, December 1955)that Lucile and Cosmo (joined by "Franks")occupied a small table in an alcove in Titanic's restaurant.
For those interested I'll quote what Lucile has to say about that now legendary last dinner in Titanic's restaurant April 14:
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(Discretions and Indiscretions, pp 165-166)
"...I remember that last meal on the Titanic very well. We had a big vase of beautiful daffodils on the table which were as fresh as if they had just been picked. Everybody was very gay, and at neighboring tables people were making bets on the probable time of this record-breaking run. Bruce Ismay, Chairman of the White Star Line, was dining with the ship's doctor next to our table, and I remember that several men appealed to him as to how much longer we should be at sea. Mr. Ismay was most confident and said that undoubtedly the ship would establish a record.
Further along the room the Wideners and the Thayers were dining with the Captain and others and there was a great deal of laughter and chatter from their table. It was the last time I saw them. At another table sat Colonel Astor and his young bride. They were coming back to New York after a honeymoon in Europe and I thought how much in love they were - poor things, it was the last few hours they were to have together. They were joined by Isidor Straus and his wife. These two so openly adored one another that we used to call them "Darby and Joan" on the ship. They told us laughingly that in their long years of married life they had never been separated for a day or night..."
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Randy