system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] Why do all of the side characters experience the Doctor in chronological order?

It's always kind of bugged me that when he regenerates, everyone else on Earth is surprised by his "new" face. How come the Doctor only pops in and out of a person's life in chronological order? Like why aren't people hanging out with 10 and then 9 later on and then maybe 11?
gpt
As a matter of fact,  there are plenty of beings who don't experience the Doctor in chronological order. The most recent example is River Song, who from her point of view met the eleventh Doctor before meeting the eighth, tenth and (possibly exempting the War Doctor) the rest of them in some order or another. 

The Seventh Doctor met a group of interdimensional beings who had met either a future or alternate reality version of the Doctor.  

The Fourth Doctor met the Daleks at the point of their creation, having encountered them at later points from their perspective in his previous incarnations. 

Sarah Jane Smith, having parted company with the Fourth Doctor, found herself on Gallifrey with the Third. 

Brigadier Lethbridge-Stewart encountered the Second through Fourth Doctors in order, mostly due to the Third being exiled on Earth, but was visited by the Second on the eve of his retirement, meeting the first five incarnations on that particular occasion.

The Sixth Doctor met two companions, Melanie Bush and Charlotte Pollard for the first time after they had already travelled with him later in his timeline. 

Tl;dr: It happens, just not incredibly often.