Taking a sharp left turn - how many Tardises are actually 'out there' at the moment.
Surmising that The Time Lords mostly withdrew to Gallifrey and their Tardises were destroyed in the attack, we still know The Doctor now has hers AND The Master's.
Any more ?
She doesn’t have the Masters anymore. Odds on he got it back after taking the long way round, and you have to ask how that hologram was made.
Rest of the universe? Well, assuming we go by onscreen only, and if we don’t have good reason to *know* they went elsewhere, there’s five, maybe six. We don’t know what happened to Chronitis’ one, The Monk has a cramped one somewhere, The Master has one, though there’s a possibility he nabbed another, and The Rani has one, and there is Clara.
If we go into the apocryphal and ancillaries, it gets more complex. There’s Compassion and Rodan possibly, I think maybe a Doctors Tardis from a parallel dimension where the Doctor died (no, not in Interference, Blood Heat.) and whatever Faction Paradox left about the place. Does Brax have one? Where did he park it? I am not into Big Finish.
It gets more interesting when you think there are some periods in human history where the Tardis is on earth more than once (‘our’ Tardis, as it were) sometimes along with their respective Doctors, sometimes not, and sometimes it appears to have been borrowed. It’s regrown itself at least twice, and we don’t know that Missy’s ‘vault’ prison, wasn’t in fact just her Tardis with its locks changed and demat circuit yanked. In which case, it may still be in Bristol.
This is just off the top of my head of course.
Compassion was awesome.