Sometimes two souls are reincarnated together, like Ross and Demelza 'Poldark' who returned in the 20th Century as 'Greg and Dharma' Montgomery.
Sometimes the physical form that houses these souls is also recreated, like the Sam and Darrin Stephens of the Tooniverse (the opening credits of 'Bewitched' and an episode of 'The Flintstones'). However, it's more important that the basics of their personalities are recaptured and hopefully improved upon in the next incarnation.
Lady Clemency Eddison and her husband, Colonel Hugh Curbishley, hosted a garden party at their estate in 1926, according to the 'Doctor Who' episode "The Unicorn And The Wasp". It was the events of that weekend which triggered the disappearance of Agatha Christie - at least in Toobworld.
A few years later, it's the contention of Toobworld Central that Colonel Curbishley passed away; his death was probably hastened by the murder of his son during that tragic weekend. Lady Clemency probably outlived him by at least another decade or so.
As such, the Colonel's soul was reincarnated first, sometime around 1934. And in this incarnation, he came back as Trevor Squires, who would grow up to be a horticultural expert at Kew Gardens. A little more than a decade later, the soul of Lady Clemency was reborn into Toobworld as Rosemary Boxer, who also became a horticultural expert.
After being sacked from the University of Malmesbury where she was a lecturer in applied horticulture, Rosemary teamed up with former policewoman Laura Thyme to run their own landscaping business. And occasionally solve murders on the side - this may have sprung from her previous incarnation's passion for the mysteries of Agatha Christie.....
Trevor Squires was an old friend and one of her mentors in the field. And as we saw in an episode of 'Rosemary & Thyme', their souls were once again reunited - but not as lovers in this go-round.
Near the end of that episode, the sins of Colonel Curbishley may have come back to haunt him. He deceived his wife into thinking that he was crippled, for fear that Lady Clemency might leave him. And when Rosemary Boxer might have needed his protection the most as they tried to escape the killer, Trevor Squires' leg betrayed him and he was left behind, slightly hobbled.
Somewhat appropriately, considering that they were once united in an episode of 'Doctor Who', the name of the 'Rosemary & Thyme' episode was "Seeds Of Time"......