Background:
Of the following possible constructions, I found explanations of 1A, 1D and 2A in grammar books.
(1A) Er hat mir einen Brief schreiben können : He was able to write me a letter (and so did).
(1B) Er habe mir einen Brief schreiben können.
(1C) Er hatte mir einen Brief schreiben können.
(1D) Er hätte mir einen Brief schreiben können : He was able to write me a letter (but didn’t).
(2A) Er kann mir einen Brief geschrieben haben : He may have written me a letter.
(2B) Er könne mir einen Brief geschrieben haben.
(2C) Er konnte mir einen Brief geschrieben haben.
(2D) Er könnte mir einen Brief geschrieben haben.
Question:
Are the other constructions also possible, and if yes when would you use them?
My random thoughts:
For what they are worth (for stackexchange says, 'Share your research').
(1B) Can 1A become 1B in reported speech? (Of course, 'er' and 'mir' may have to change.)
(1C) Could 1C be like 1A except as happening at a time prior to a given past. For instance, I was prepared yesterday because the day before he had been able to warn me.
(2B) Can 2A become 2B in reported speech?
(2C) Could 2C be like 2A except as happening (being the case) at a past time. For example, as of yesterday we all entertained the possibility of his having written me. Today, we know that he did or did not.
(2D) Could 2D be like 2A but the speaker feels more uncertain?