I believe that makes sense. You may judge below!
I do my very best to make sure everything is as historical as possible. The secrets post, for instance, was not particularly well-written, but those were his living and boarding arrangements, as recorded by his 'landlady,' along with other personal habits. I know what tuberculosis was like from accounts and medical books of the times, and what John's night would have been like, in terms of symptoms. I know he was friends with Addie, because he, acting alone, saved her house in the town plot skirmishes, and in her testimony, she recognised him walking down the street with the Earps, but failed to identify Wyatt or any of the others. She was Josie's good friend, so John must have had some relationship to her thus, apart from Wyatt. His thoughts are feverish in the post, of course, but reflect what Gillie said about John and Wyatt's parting.
It is true I extrapolate, because so much is not known, but I make sure everything he says or does or thinks is possible, given whatever information I have, which is by now a great deal.
Roleplaying is different of course, because I can only try to feel what he would do or think or say, given what I know and the small examples of his diction that was recorded. It is extrapolation especially as he is happy now, as he never really was. Gabriel has solved most of his darkest worries, confirming Heaven and Wyatt's love and his mother's pride and Mattie's faith, and he knows he will see them all again after he dies, and that Gabriel will be there and his loved ones always. These things make an enormous difference. Some of his ideals were demonstrated rather than spoken, but he obviously held them perfectly conceived because he consistently and firmly acted in accordance with original and unpopular codes.