We know that Msgr. Lefebvre did not believe it - but there is no good reason to suppose Cardinal Ratzinger was lying about the date. You talk about "other phony projections": perhaps you can list some of the dates for the episcopal ordination that Cardinal Ratzigner agreed to and then reneged upon later? But of course such accusations have no proof behind them, just suspicions and claims that the Pope was "out to kill the old Mass", something quite untrue.
If you can't show the actual offer by Ratzinger
That was an offer! Ratzinger said that the consecration would be August 15th, and asked for candidates. Msgr Lefebvre was the one who refused to work towards the ordination, insisting that all three of his rejected candidates be made bishops instead of submitting new candidates as the Cardinal requested.
The motu proprio promised that the two missals could not be mixed
You are thinking of the conditions attached to the 1984 indult.
that the FSSP would have "exclusive" use of the '62 missal
You quote "exclusive". Perhaps you can point to where "Ecclesia Dei" says "exclusive"? Actually what was granted to the FSSP was the right to continue the use of the 1962 MR, but nothing in the Missal takes away the right of the FSSP clerics to say the Mass according to the reformed rite if they so wished - and this is all Protocol 1441 said. Nothing obliges FSSP clerics to say the reformed rite - and this is quite obvious from the fact that the dire predictions made during the controversy over the Protocol have not come to pass.
You are the one claiming Ratzinger proposed a definite date. But you offer as proof the letter by Lefebvre laced with sarcasm about the Cardinal's insincerity in demanding dossiers--which would have delayed the process still more and was still more evidence of insincerity on the part of Ratzinger. So I ask again--show me where Rome ever proposed a definite date. And why, if Rome was sincere, were the names the Archbishop proposed, refused?
Rome in the past had routinely accepted even the names of suspected perverts named by archbishops, or even of outright known apostates. It demurred apparently only when Lefebvre proferred names--though he alone would have best known which men could be trusted to hold the line against papal pressures in the future and which would not. And this is precisely the point. Rome had an interest in appointing weak men who would do its will, the Archbishop had an interest in preserving Catholic Tradition at all cost by naming only the most committed.
Add to this problem of who to name, the papal "commission" which was also about to be set up and which would mean that traditional Catholicism would be controlled by Rome herself --and you can see the dangers that were being proposed for Lefebvre's acceptance. In fact the Ecclesia Dei Commission even now has proven no genuine friend of Tradition, having already punished the FSSP by firing its superior general and several of its theologians for what it perceived as an affront to the conciliar Church--in other words, for very minor offenses.
As for the issue of exclusive use of the missal, I was alluding to the ninth footnote which referenced "Quattuor Abhinc Annos," Oct. 3, 1984; AAS 76 (1984) pp. 1088-1089. This letter required that "These celebrations must be according to the 1962 Missal and in Latin" and that "There must be no interchanging of texts and rites of the two Missals." This was reinforced afterwards by the Decree of Erection which was given in Rome by the Pontifical Commission Ecclesia Dei on 18 of October 1988.