The assumption that Susan would not the 5 Doctors episode because Sarah Jane Smith did not recall it has one flaw - School Reunion suggests Sarah DOES the 5 Doctors episode.

When Sarah remarks the Doctor has regenerated the 10th Doctor replies that he has regenerated 'half a dozen times since we last met" in other words, six times.

Six regenerations back from the 10th Doctor means you have to go back to the 9th, The War Doctor, the 8th, the 7th and the 6th - arriving at the 5th.

When did Sarah Jane meet the 5th Doctor? In the 5 Doctors story.

It may be possible that the Doctor re this and Sarah does not - but the point is worth considering, I think.